Satan has possessed my computer

Here are the symptoms:

The computer will power off during these situations randomly.
1. During POST Screen
2. While Windows is loading
3. Just after windows has loaded to the desktop
4. If I launch a computer game (w/ 3D graphics) shortly after windows loading and the comp. had been turned off for a while.

Once the "power offs or shutdowns" occur I'll have to try and restart my comp. 5-10 times before it will fully load to the desktop without crashing and powering down.

This problem occurs randomly and has exsisted for over 6 months.

The second problem relates to the harddrive:

When the HD starts to boot right after BIOS it will make a "whooSHHHHH...TOCK!.....whooSHHHH....TOCK!" over and over again with a varying rythm. Needless to say windows won't load and it usually just sits dead at the POST screen. Also If I reboot and F2 into BIOS the HD isn't detected.
This same "whooSHHHHH....TOCK!" sound also randomly occurs when I play certain games (Call of Duty, Far Cry) the computer locks up and the HD continues to make that noise until I power down. Then it usually does the same thing when I reboot.

Both of these symptoms seem to occur at random but usually follow one right after the other.

After speaking with a few people they have pointed to my PSU as being the source. Its a generic 400W that I picked up cheap ($40) and have been using for over a year and a half.
BIOS Hardware monitoring reports:
+1.5V in 1.467
Vccp 1.435 - 1.447
+3.3V in 3.275
+5V in 5.078
+12V in 11.875

My system specs:
P4 2.53 533FSB
Intel D845PEBT2
512MB PC2100 (266Mhz)
ATi 9700 Pro
SB Audigy Gamer
WD 800 (80GB, 7200RPM, 8MB cache)
Generic 52x CD-Rom
Philips CDRW4000
1.44 Floppy
4x 80mm case fans
WinXP Pro (fully updated)

Does anyone know the root of these symptoms? And is it infact my crappy PSU.

EDIT: I've checked the HD many times with Western Digital's DataLifeguard Diagnostic tools on many occasions and the drive reports no errors. Plus it has the correct jumper setting, cable, and snug connection.

 

I had a very similar problem last year - computer hanging or rebooting randomly at various different points. Sometimes I'd get to use it for 5 minutes before it rebooted, sometimes only for 30 seconds, and like you, I often had to restart 5 or 10 times. Someone suggested that the problem might be with the motherboard (an ASUS A7N8X Deluxe) so I borrowed a mobo from a friend and tried it - problem solved. No more random rebooting. I took the mobo back to the shop and replaced with a Gigabyte 7NNXP which has worked great for the last 9 months. Apparently a lot of people had the same problem as me with the ASUS A7N8X. I'm far from being a hardware expert, but you've got the same symptoms as I had, so it might be worth borrowing a different model mobo and seeing if it works. Good luck

 

Well, in my honest opinion!!!! Hard drive is bad. Don't quote me but I have had a few WD drives go bad recently and the data lifeguard tools say the drives are fine. Same exact noise you are describing and issues as well. The power supply could also be the root of the problem. Again in my opinion and through trial and error. This is a hard one to pin point unfortunately.