My machine simply won't turn on . - KitchenAid KSM103 Professional 5 Series Stand Mixer

The kitchenaid warranty is exactly 365 days from date of registration "No Questions Asked" on day 366 you have no warranty and you gotta pay.
Now the good news; first check the wall socket, I know it works but check it anyway. then check your plug, did you step on it while you were working on the machine? The plug often falls to the floor during work and can get underfoot, you may have broken the plug it'self. next you will need a parts list for your model from Kitchenaid's website.
http://www.kitchenaid.com/customer-service/manuals/
My first suggestion is to try a minor adjustment of the speed control switch, they often get out of sync when you do something to the machine. You can find several videos of this on the youtube site. "Adjusting the speed control switch on kitchenaid mixer"
If the two or one of the top 2 screws on the speed control switch move it can shut the machine down just like an on/off switch. Did you remove the back cover during your adjustments? Did you remove and replace the carbon brushes on the side of the machine while working on the machine? If you did you might have put them back in incorrectly, if you did they will also act a a shutoff switch. If you did not take them out then DON"T as there are four ways to put the brushes back in and only one way is correct and there are two brushes to deal with. Has work ever been performed on the mixer before? Because if all you did was to adjjust the beater height screw then nothing should have effected the normal operation of the mixer. So if there is anything that you did but did not include in your description of work you performed then please let us know. We strive to give accurate solutions but... as I am a KA tech I do not have any other solutions with out the machine in front of me. Just so you know you can fix this yourself.

If the mixer died completely and no noise at all comes from the machine you need one of three things.
1. New brushes2. new speed control switch3. a new motor.

The KP26 is a 6 quart mixer of the new design, post 2002, it is easy to work on and relatively inexpensive for parts if it turns out to be the motor that will be about $100.00, the speed control about 30.00, the brushes on this mixer cannot be replaced you have to install a new motor, sry about that. Hope this helps let us know. But first check that the electric outlet you are working from has not tripped the breaker on the circuit too. I know I know it's silly to say but check the outlet first before you spend a dime on anything.

bread is very tuff on mixers. always buy the strongest mixer that you can afford. im guessing the field in the motor fried.

Check carbon brushes, check for broken wires under back cover.

This particular model has some sort of internal electronics that require a charge before the unit will function. As a result, when allowed to sit in the cabinet for a long period of time it will simply not turn on. Instead, all you will hear is a "click" noise when you try to power it on. When you get the dreaded "click" noise leave plugged in for several hours and try again.

take it in to an appliance repair shop for a proper diagnosis and quote but it is probably not worth repairing ( armature and brushes )

Obtain a copy of the Repair Part List for your model from Kitchenaid.com.
Download a Copy of the Kitchenaid Service manual.

http://www.kitchenaidparts.be/centers/servicemanual/mixer.pdf

First, you may want to adjust the mixer's speeds:

1. Loosen the lock nuts enough & Turn the 2 top screws clockwise until they cannot be turned
anymore. Leave the bottom screw alone for now.
2. Use a dab of white paint or paper whiteout to mark the positions of the Phillips screws.
3. Plug in your mixer and Set the speed selector to "Stir".
4. Turn each top screw One full turn couterclockwise (alternating between Left and Right)
Keep making one full turn at the time (for both left and right) until the motor starts running.
5. Put your hand near the Agitator shaft and allow it to brush your finger slightly. Use your
watch or clock and start counting the number of times the shaft touches your finger in
60 seconds. The correct count should be 60 RPM (Rounds Per Minute). If it is less
or more than 60, give each screw 1/4 turn counterclockwise or clockwise and start counting
again. Now tighten both lock nuts.
6. Set the speed selector to "6" and turn the bottom screw either clockwise or counterclockwise
to achieve a speed of 180 RPM.

For your reference, the planetary RPM's for the 5-qt. tilt-head Artisan Stand Mixer are as follows:
Stir speed - 60
Speed 2 - 95
Speed 4 - 135
Speed 6 - 180
Speed 8 - 225
Speed 10 - 280

Second, if the mixer won't run:
Remove the Control Plate Assembly (36), the Phase Control Board (39)
and the motor Governor Assembly (35). Inspect for loose connections,
burnt or damaged components. If they seem to look OK, re-assemble
them and test the mixer. If the motor still won't run, then I might suspect
a defective Phase Control Board (39).

Get a copy of the Repair Part List for your model at Kitchenaid.com
On each side of the Motor Housing(1) is the large black Brush Motor
Cap(23). Each Carbon Brush(19) is keyed (one corner is not square)
and is designed to go into the Motor Housing slot but only one way.
Each Carbon Brush must make contact with the Motor Coils. The
motor will not turn if one or both does not come in contact with the coils.
If the brushes are too worn out, of course they won't touch the coils
neither and your motor will not run. You can purchased new brushes
on Ebay if they need to be replaced.

The Speed Control lever is linked to the Speed Link mechanism, which in turn moves the
Speed Control Assembly to allow the motor to operate at different speeds.
Get a Repair Part List from Kitchenaid.com for your particular model to see how it works.
As you select different speed setting, the Speed Link simply moves forward or backward,
thus pushing the Speed Control Assembly back and forth.
If you cannot move the Speed Control lever, means that the Speed Link is somehow bent
or out of place. Remove the Motor Housing and the End Cover and check it out.