I am assuming you have tried new ide cable...
I'd suspect board failure, less likely cpu. You DID turn off any overclocking, right? I've found often that loading overclocked leads to trouble, and always run at default speeds for loading OS.
Does the board act properly if booting sans ram or cpu, vga card? In other words, correct bios beeps? If no beeps, that will show the mobo is hurt.
Wouldnt hurt to also run memtest, although longshot, bad ram will introduce funny symptoms.