Inverter Crisis!

I have a 2000 watt Vector inverter and the only time that what your saying happens to me is 1. You have to many things running at one time and are running the inverter over it's designed capacity 2. The inverter is not grounded properly 3. The cables you have going from the inverter to the battery are to long. As cable length increases voltage decreases .
4. You have to many power accessories running at one time. Shut everything down before using the inverter. Also, Are you sure the microwave is only 800 watts ? Just because the box of a microwave says 800 watts of power does not mean that is all the power is draws.
A microwave advertised as 800 watts might actually be drawing 1000 watts or more.
I hope this helped you.. God bless you !