How did you connect the PC to the plasma?

1. If you are using long VGA cable, try to replace it with a better one...(standard VGA cables are good for only 1.5 meters run...)

The best way is to use a VGA to 5 BNC adapter (short) connected to your PC, and then run 5 RG59B/U video cables to your Plasma (for runs > 5m), or a multicore (5) video cable.

2. If you are using the TV OUT(composite or S-Video) output of your PC's VGA Card, try to replace the card with a better one...

For me, the first choice works always perfect.

Hope this will help...