Thanks to a very helpful Devon Kerr I now know what parts of my PC were causing my prior trouble.
I was running a Core 2 Duo 3.0GHz LGA 775 in an Asus Striker Extreme mobo with 4GB of DDR2 800 RAM.
I played around with every possible video card and ram combination (since I had multiple’s of each) and had pretty much ruled those out.
Devon was kind enough to provide a Core 2 Duo 1.8GHz CPU, some XMMS RAM, and an ASUS P5B deluxe.
I swapped out my RAM for his RAM, no go.
I swapped out my CPU for his CPU, no go.
I swapped out my motherboard for his motherboard, CPU, and RAM – system fires up.
I put my CPU into his motherboard and RAM – no go.
Put back in his CPU with my RAM – system still works.
Problem identified: 1 x Bad Mobo, 1 x Bad CPU. Really unexpected, but that’s what it looks to be. My mobo won’t work with a known good CPU, and his mobo won’t work with my CPU, even though all compatibility checks out.
Now what to do? I have enough components now for a slower (but working) desktop solution. Maybe instead of buying replacement / upgrade parts I’ll just leave things like they are until something else dies. Either that or go all out with new CPU, Mobo, and RAM.