Garbled screen on startup, what next?

I have an older Dell Optiplex GX620 with Win XP Professional. I have the product key but no media disc. Today the PC gave me a bunch of garbled characters when I started it, can't tell if it's the GPU that failed, or the motherboard, or something else. I can't seel what it's doing when I start it up, it doesnt make the normal startup sounds, and no dice trying to get it to boot up in safe mode (F2, F8, F12, etc).

I'd just replace the computer but it's running some CNC equipment and I don't want to deal with re-installing all the programs and dialing in all those settings again. Would much prefer to just fix the issue on this dinosaur if possible.

I surprisingly found what appears to be the same motherboard for sale through PriceBlaze, but I have some concerns:

1. What are the chances this will resolve my problem?

2. Will I have to re-install Win XP? If yes, I fear this will wipe out my existing CNC programs and their settings.

3. I have the Win XP product key but I don't have a media disk, will this present a problem for me?

Appreciate any help you guys can provide.