Bought Platinum MSI ATX mainboard, Geil 2GB Dual RAM, E6600 CPU, Raptor disk. Have had an interesting experience...

HISTORY:
PC started crashing, after a year the Raptor disk died (metallic sound and no boot/access), when I used then only 1 RAM chip at slower than specified latency, it crashed less. Eventuelly it crashed more. I replaced RAM, PC worked fine for a few days, then started crashing. I switched PSU (from 400W to 200W), it crashed less, but suddenly no more boot (just fan on/off sound). The old 400W PSU had a tendency to restart fan at boot, like a faulty engine start. No problem with "new" 200W PSU ("new" PSU I've used for 7 years with Athlon - never a problem).

Got new mATX mainboard, worked super for 1 week. Then new raptor died in the same way. Got new raptor disk. 2 days later, no boot with new mainboard. But then I switched RAM banks, so RAM chip 2 is in bank 1 at the moment and everything is perfect. BUT I expect this will not last...

Any idea of the source of the problem? Should I replace everything as maybe mainboard destroyed ram, and then the destroyed ram will destroy new mainboard and maybe CPU and PSU, so best to replace everything to avoid "infection" from faulty parts?

For starters, you need at least a 600 Watt Power Supply Unit. 200 Watt will barely run a 486DX Mainboard and a 400 watt PSU is for Pentium 3 Main boards.

Are you using DDR400 Ram?