2000 watt cobra inverter keeps saing olp, overload

Assuming you have a 12VDC In 120V AC out 3000W inverter.
LUP indicates battery voltage is low, so firstly make sure:

1. You 12V battery is good, it's large enough a minimum of 75AH and probably much larger is recommended and it's fully charged.
2. Verify you are using the correct size copper wires from battery to the Inverter DC INPUT(s). If you keep wire short the wire size can be smaller, but if the DC input wires are longer then you will need to use thicker copper wires.

At MAx load you would be taking 250 AMP from battery, so for a 5% Volatge drop of .6 V for a 10 ft length of cables from battery to Inverter you would need to use a 1AWG copper cable.

http://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=0.4066&voltage=12&phase=dc&noofconductor=1&distance=10&distanceunit=feet&eres=125&x=37&y=8

OLP is a overload condition, which means you may have to many high powered AC powered things connected to the Inverters AC outlets or maybe something that has large start up surge, ie devices large electric motors.

Or it could be all due to a faulty Inverter.

Instantaneous surge current can trip the breaker. You need to look at the data plate on the oven to see what the actual draw off the mains is. 700 watts of microwave power is NOT the amount of power drawn when it starts. You have the fan motor and the tray rotator motor to deal with when calculating the correct size of inverter to use with it.

The olp overload refers to Watts and the fuse is monitoring Amps! The rule is replace fuses with the same or lower but in this case it isn't causing the olp!

find the watts on each appliance. Usually on the back of then. Add all the watts together then buy a inverter that can put out more than what you need. Say all the watts come up to 2,000watts you will need an inverter that's 2,500watts minimum so you don't burn up the inverter.

Its an inverter DC to AC---what since I do not understand the described problem is the unit doing or not doing?

If your freezer need more than 800 watts to run then your 800 watt inverter will be overloaded and it will shutdown.

You may not have adequate input voltage. And unless you are hooking up to a forklift battery, the battery will not have adequate current delivery capability for any more than a few seconds at full power of the inverter.

1200 Watts is 100 Amps. 1500 Watts is in the neighborhood of 130 Amps.

With inverters and generators, the power rating is usually off by about a quarter.
Watts and volt-amperes are totally different and sometimes inverter manufacturers don't tell about the difference. A basic rule of thumb is to take whatever the inverter is rated for and knock a quarter off. So, in your case it would be best to assume a maximum rating of 1500 watts.
Also, inductive loads like drillers (electric motors) usually have a start-up current 3 to 8 times the rated operating current. Meaning that 100 watt driller will draw 300 watts to start up. So, if you use an electric motor rated at 700 watts, its startup load would be 2100 watts or even more and thus trigger the inverter overload switch. Hope this helps you.

There are 8 40A fuses inside this unit. In the following pics you will see a bank of 4 and another bank with 3 of the 4 removed. I'm currently working on mine as it will cost me more to ship and have Cobra repair than I paid for the unit ($133 to repair). Good luck with your problem

got a cobra cpi 480 inverter it keeps beeping everything runs but produces no power