Microwave won't heat up while in use

Many factors at play here. Are you cooking on the range? Are you using the microwave? Is the light on?
There is very little current going to the touchpad and if there were a short in it the touch pad would not work. It is just heat from another source. Don't worry about it.

Hello - Interior cleaning after convection, mix or broil cooking:

Spatters may occur because of moisture and grease. Wash immediately after use with hot, soapy water. Rinse and polish dry. Harder to remove spatters may occur if oven is not thoroughly cleaned or if there is long time/high temperature cooking. If so, you may wish to purchase an oven cleaner pad with liquid cleaner within it-not a soap filled steel pad-for use on stainlessor porcelain surfaces. Follow manufacturer's directions carefully and be especially cautious not to get any of the liquid cleaner in the perforations on the wall or ceiling or any door surfaces. Rinse thoroughly and polish dry. After cleaning the interior thoroughly, residual grease may be removed from the interior ducts and heater by simply operating the oven on 450 F for 20 minutes without food. Ventilate the room if necessary.

Interior cleaning after microwave cooking:

Cleaning is easy because no heat is generated to the interior surfaces; therefore, there is no baking and setting of spills or spattering. To clean the interior surfaces, wipe with a soft cloth and warm water. DO NOT USE ABRASIVE OR HARSH CLEANERS OR SCOURING PADS. For heavier soil, use baking soda or a mild soap; rinse thoroughly with hot water. NEVER SPRAY OVEN CLEANERS DIRECTLY ONTO ANY PART OF THE CONVECTION MICROWAVE OVEN.

1. Fill a plastic bowl with 1 qt. of warm water. Add 2 tbsp. of liquid dish soap and 1/4 cup of chlorine bleach to the water. Thoroughly mix the solution.
2. Dampen a clean cotton rag in the solution. Wipe all inside surfaces of the microwave with the soapy rag to remove food debris and stains. Scrub stubborn residue with a nylon scrub brush.
   
3. Moisten another cotton rag with warm water. Wipe the microwave surfaces with the rag to wash away soap and loose food debris. Thoroughly rinse the inside of the microwave.
4. Dry the microwave's interior surfaces with paper towels. If odors remain in the microwave, fill a microwave-safe bowl with 1 cup of cool water. Add to the water 2 tbsp. of baking soda, half of a chopped lemon (including pulp and rind) and four whole cloves.
   
5. Place a microwave-safe plate on the microwave turntable. Set the bowl on the plate.
6. Heat the microwave on high for three minutes. Operate the microwave according to the manufacturer's directions. Keep the bowl in the microwave for 15 minutes.7
7. Remove the bowl from the microwave. Wipe the microwave's interior surfaces with clean paper towels to remove steam moisture.
8. Leave the microwave door open overnight to completely air out any remaining odors.

HELLO.

Solution to your microwave problem is given as below.

* 1 Set your Daewoo microwave on a countertop near an electrical outlet and plug it in. Open the door and place the circular roller guide in the center of the oven cavity, then place the glass cooking tray over it.

* 2 Set your food on a microwave-safe dish and then put the dish on the cooking tray and close the door. Make sure that it latches properly.

* 3 Turn the upper knob to select a power level. Power levels include "Defrost," "Med-High," or "High." If your Daewoo has a touch pad, touch the "Microwave" button once to set the highest power level. Touch it consecutive times to lower the power level.

* 4 Turn the lower knob to set the cooking time. For cooking times less than two minutes, turn the knob up past the two-minute mark, then back to the correct time. For touch pad models, enter in the cooking time with the numerical keys and then press "Start."

* 5 Open the door at any time to stop the cooking and check the temperature of your food. Shut the door to automatically continue cooking, or turn the timer knob to the right to add more time. For touch pads, press the "Stop/Clear" button, then key in a new cooking time and press "Start."

* 6 Open the door when the timer reaches the "Off" position and take out your food.

Thanks.

HELLO.

The code on the screen indicate electric panel fault resulting from the touchpad malfunction.

The touch pad on your microwave oven acts as the brain of the appliance. It not only contains the buttons that you use to enter cooking settings and times, but also controls the function of the entire microwave. If the touch pad malfunctions or breaks completely, the microwave will cease to function. In this instance, the broken touch pad must be removed and a new touch pad must be installed, to restore functionality to the microwave.

1 Unplug the microwave from the wall outlet.
2 Remove the two screws, located on the front or top of the grill at the top of the microwave.
3 Pull the grill off of the microwave.
4 Remove the mounting screw from the top of the control panel.
5 Lift the control panel up and out to loosen. Look behind the control panel to ensure there are no metal tabs securing the control panel in place. If there are metal tabs, gently rotate the control panel to free the tabs.
6 Transfer the wires from the old control panel to the new control panel one at a time to ensure that the wires are properly installed.
7 Install the new control panel into the microwave and secure using the mounting screw that was removed.
8 Replace the grill from the top of the microwave and secure it using the screws that were removed.
9 Plug the microwave back into the wall outlet.
Thanks.

Rust can form from the steam and condensation as you say, and it's a good idea to always cover food and wipe the oven out after using it. You can sand off the bad paint and rust the same way you can on a car, and then touch up the paint if it's a minor amount. Spray paint specifically made for microwave cooking cavities is available. (You don't want to use paint that may have metallic components.) It may be available locally if you have appliance parts stores in your area, and you can find the paint online as well. There's no need to replace the oven just yet, unless you find a good deal on a new one and you're looking for an excuse.

DO NOT use SOS pads! They are made of STEEL WOOL and will remove the protective finish inside the oven cavity. Without the protective coating, the microwave can arc internally and ruin the magnetron. Use the green scrub pads you find in the dish detergent section of your local grocery store. They are considered non-abrasive. Use the green scrub pads along with a non-abrasive cleaner such as Soft-Scrub or 409. Wipe clean with a fresh water and dry with a clean cloth.

this feature allows you to program your oven to begin cooking automatically at a designated time of day. Simply touch Custom Help pad. Touch the number 3. Enter the start time. Touch Clock pad. Enter cooking program. Touch Start/Touch On pad.

Direct spraying of cleaners on the keypad and steam from the cooktop can short the keypad.

Luckily, it dried out. Sometimes it doesn't, and the keypad has to be replaced.

I always recommend that you spray non-ammonia cleaner on a soft cloth (not a paper towel which can scratch) and gently wipe the keypad.

And I always recommend that you use the vent fan when cooking on the stove top to keep heat, steam, and grease out of the controls.

We're happy to help you with free advice and we'd appreciate your thoughtful rating of our answer.

From GEAppliances.com: Microwave - Cleaning Recommendations To minimize the possibility of electric shock, unplug the microwave from the power supply before attempting any maintenance or cleaning. Spills and spatters clean up easily with a damp, soapy paper towel or sponge. It is best to clean soil as soon as it appears. Baking soda and water may also be used. If the food has cooked onto the interior, heat one cup of water on full power for three minutes. The heat and steam help to soften the food. After the three minutes, allow five additional minutes stand time then clean as usual. A non-abrasive scrubbing pad cleaner works well for stubborn stains. You may use mild dish washing liquid or cleaners specifically listed for cleaning interiors of microwave ovens such as MicroBryte® (wx10x3030) or Microwave Oven Magic®. We do not recommend using other detergent based cleaners because they can cause the plastic parts to crack. You may purchase microwave interior cleaner by calling our parts department at 1-800-626-2002, on-line from GE Parts or from your local grocer. For stainless steel interiors of microwave/convection models, we recommend a plastic, soap-filled scouring pad. Rubbing gently with this pad will help remove soil. For the door surfaces (both interior and exterior) We recommend you use only mild, non-abrasive soaps, or detergents applied with a sponge, or soft cloth. For the control panel Wipe with a soft, damp cloth. Dry immediately with a soft cloth. Do not spray any solution directly onto the controls Important: Commercial Oven Cleaners, abrasive cleaners, or cleaners containing ammonia or bleach (can make the plastic brittle) should not be used on any part of the microwave. -- From me - Maybe local restaurants in your area would have some tips? Otherwise, try a Google search for keywords: cleaning stainless steel oven