Start with a basic "walk-around" inspection to check for any obvious problems such as loose wires or cables, visual damage to the unit and appropriate fluid levels. If your portable generator still isn't producing power, stop the engine, allow your unit to cool down and try the following:

RP Series
1.  Reset the circuit breaker on the generator (see Owner's Manual for instructions) 

1. RP5500, RP6500 E, and RP7500 E Owners Manual
2. RP12000 E Owner's Manual

2.  Reset the GFCI (see picture below)
3.  Plug in a different device or power cord
4.  If your portable generator still isn't producing power you can try to field flash (see the Service Manual)

1. INV2000 Service Manual 
2. RP5500, RP6500 E, and RP7500 E Service Manual
3. RP12000 E Service Manual

INV2000 
If the inverter overload LED (middle LED at top of control panel) is solid red, the generator will shut down the output power, but the engine will continue running.
1. You must turn the control knob to OFF and allow the engine to stop for several seconds.
2. Restart the generator using the steps in the quick start guide.
3. Confirm that the overload LED is no longer lit. If it is no longer lit but you still don't have power follow the steps below:
   a.  Reset the circuit breaker on the generator (see the INV2000 Owner's Manual for instructions) 
   b.  Reset the GFCI (see picture below)
   c.  Plug in a different device or power cord
   
If none of these steps fix your problem, call Customer Support at 1-844-PWR-MEUP (844-797-6387) or take your unit to a local Cat Home & Outdoor Power Authorized Service Center.