It's not the CPU... *breathes a sigh of relief*
I took the CPU and put it into the spare machine I had. It has an ASUS motherboard in. After a few chops and changes, it works. I thought it was the screencard again, 'cos it was doing the same thing it did last time before the screencard died, but after pulling everything out and reseating it, it came on and started up.
I just need need to put the other RAM module in, and then it's sorted. I'll build it over into my Thermaltake box this weekend.
At this point in time I'm not sure whether I pulled some cable out on the LANParty motherboard that wasn't supposed to be pulled out, or whether it's really konked. What's important is that my PC is working, sort of... and that makes me happy.
This motherboard isn't too shabby... it's not the LANParty board, but it works...
Thanks for all the help guys, I really appreciate it.
I'll investigate some more over the weekend... maybe it's just an unplugged cable on the other machine, but somehow I think it's worse than that...