Cannot boot up/I think it is PSU

[j press]

Got a little problem.

System:
MOBO - Asus A7N8X DX
CPU - AMD Athlon XP 2800+
512M PC2100 RAM
2 x 60G HDD
Plexor CDRW
Plexor DVD+-RW
Nvidea GeForce4 128M Video card
400W Power Supply
Cheap Mini ATX case
APC Back up power supply

The system is over a year old and is running Wondows XP Home and has had only minimal problems throughout its life that I could easily fix.

Problem: Last 4 or 5 months, the power fan has been making a buzzing or grinding noise for the first 5 or so minutes after start up. I can hit the fan and if I hit it hard enough it will stop making the noise (yes it is still running).
A few days ago I removed a virus off of it and from then every time I shut down the computer it would reboot itself. My quick fix was to pull out the power cord as it shut down (no power switch on the back of the power supply) and before it started booting again. I did that last night and now it will not boot.

Symptom: The fans start spinning and power comes onto the system. Lights come on all over and disks begin to spin; then, after ~4 or 5 seconds it shuts itself off and starts to boot again. It does this in an endless loop until I again have to pull the power chord.

Troubleshooting: So, far I have reseated everything, tried to boot it up barebones, and tried to boot it without the reset button connected. I unplugged it from the APC and it booted up to the Windows screen and then shut down again to be in the endless loop of 5 second booting. I have tried to plug it into different outlets and with different chords and I only get the boot loop.

I think it may be the power supply surging or something related to the power.

Any suggestions?

Thanks

[CuratoR]

Yup, It maybe your PSU.

[Fruss Tray Ted]

Download your harddrive utilities and run them. If your harddrive is ok, try a repair installation with your XP disk.

Sounds to me that you may have caused some bad sectors on the HDD. If so, you may want to consider getting another drive, installing XP onto that, and retrieving your files from the one you have now.

Edit:
Now it seems you don't even get past POST so checking your RAM with Memtest may be needed too.

[classicsoftware]

First question is are you getting the single POST beep to indicate the BIOS is reading all of the relavent hardware?

Next, just an aside, it's a good idea to avoid corporal punishment where PC's are involved.

Could be the PSU and could be the motherboard. Since you smacked the PC around a little, open the case and seat and re-seat:
All Power Cables
All drive ribbon cables (both ends)
RAM chips
PCI/AGP cards


Let us know what happens after that.

By the way, is it a crime to beat your computer to death?

[j press]

No, I don't get the single POST beep or anything except for the one strange time it booted up to the Windows screen. I tried re-seating everything inside and that didn't help either.
I am going to try to hook up a multimeter to the power supply and see if it works right; however, which color would be the best to get a reading from? It looks like red gives me +5V and Yellow is +12. Is that good or is there any chance of screwing it up more with the multimeter?

Thanks

[classicsoftware]

I would just replace the power supply at this point.

[j press]

Yup, it was the power supply. I borrowed one and hooked it up and it works like a champ. Now I just need a replacement.

Thanks a lot.