Hello all! I am having some problems with my old PC which I am looking at having to replace, but would like to have your input before I start parting it out. I have two questions:

1). Several months ago I started noticing power fluctuations with my unit. When the machine would do something disk or processor intensive, the fans would slow down. The machine killed a succession of both new and old hard drives (killed the new one after about 4 months of regular use), and experienced memory problems. I replaced the ram which seemed to clear that up, but was concerned about the hard drives and the fan, so opted to replace the power supply. Removing the old PSU was a challenge, however, as apparently two of the four posts on the so-called "P4" auxiliary connector (on the clip/I/O shield side) had burned and fused with the motherboard's connector. I managed to remove it, but could not connect the new PSU there. The board powered up, booted, and appears to be stable with the new PSU despite the absence of the P4 plug, however I am still having the issue where the fans will slow (and leds will dim) under virtually any load. I am concerned about damage to the other components as a result of these fluctuations. Is there anything to do other than replace the board? I have a lot of experience in IT, but not with PCB component-level repair, and quite honestly a machine this old isn't worth enough to me to haul out the soldering kit or voltimeter.

AMD Athlon XP 2100
DFI NFII AL-400 Motherboard
1GB DDR400 SDRAM (1 piece)
PNY Geforce 5200
Gigabit Linksys 32bit PCI (installed but disabled in WinXP)
450W Coolmax PSU
160GB PATA HDD
2x Pioneer 18x DVDRW

2). Part two of my question is, were I to replace this with a modern board and system, would a 450W PSU be sufficient? I'm not out to break any FPS records and was thinking along the lines of a Intel D975XBX with a ~2.2GHz Core 2 Duo and a NVIDIA 7300GS or 6800, not SLI'd. Would I need something more like 600W for that or would I be okay? Thanks very much in advance!

I don't know much about your first issue, but you can use the following to determine your wattage requirement for the new system:

eXtreme Power Supply Calculator Lite v2.5

Add about 50w to 100w to the results you get, and you'll be good.