I think what is happening is the powersupply in the computer is bad.
That would explain the first inverter blowing fuses.
The second inverter apparently was using a higher amp fuse and wouldn't blow at first.
When it finally blew on the second one at the end it was probably from turning it off and then back on, but too quickly. I've seen mine do this before.
disconnect the PS from the computer's MB and drives and plug it into a house line, run an extension cord if you don't want to pull it from the car. See if it still sparks, smokes, or is smelling burnt. I bet it's bad.