I have a strange problem with my new build. I've searched around, but don't really know what search terms to use. Here are the parts:

CPU: AMD64 3400+
Motherboard: ASRock K8NF6G-VSTA 754
Video card: EVGA 320-P2-N815-AR GeForce 8800GTS 320MB
500W power supply
2 IDE drives
1 SATA drive

The processor and drives were actually from an old build. I can be more specific about the drives/PSU if requested.

Originally, I tried using an old 400W power supply, but couldn't get it to boot. It powered on for a couple seconds, then turned off again. I did some digging and decided that I probably didn't have enough power, so I ordered a new 500W power supply. (The video card says it requires a 450W one, so I decided to go a little higher to be safe.) So I got my new PSU, installed it, and tried turning it on (no monitor, mouse, or keyboard hooked up). Everything seemed fine. It turned on and stayed on. So then I hooked up the monitor and everything was still fine. It started booting correctly. Then I turned it off and hooked up the keyboard, mouse, and ethernet cable. As soon as I did that, it started doing the same old turn on/turn off routine. I unplugged the keyboard, mouse, and ethernet cable, and it continued to have problems. Now I can't get it to boot at all.

I'm not really sure what to make of this. The only thing I can think of is that the extra power required for the USB devices caused it to not have enough power, but that seems kind of ridiculous, especially since it no longer works even without those devices. Does anyone have any ideas on what my problem might be? I really appreciate it.

Make sure you hooked up these connectors: 4-pin cpu, 20-pin mobo, 6-pin video.

Move everything out of the case, hook them up w/o any drives, if no luck, reset cmos. If still no go, reseat cpu cooler.

What's the ram? Try one stick at a time in each slot. What's the brand & model of the 500w psu?

The connectors are hooked up correctly. The power supply is Xclio GoodPower (500W). I'll try the other stuff. Thanks for the response.

Edit: Okay, I tried hooking up everything outside of the case in various configurations with no luck. I tried resetting the CMOS. I also tried messing with the RAM with no luck. The only thing I have yet to try is reseating the CPU heatsink/fan.

Be sure to clean off the thermal paste, rubbing alcohol and a coffee filter, and apply new paste

Okay, I've tried reseating the CPU/heatsink, but still no luck. I'm not completely convinced that I'm doing it right, though.

My process is something like this:
1) Take off the old thermal paste with rubbing alcohol and Q-tips. Wipe off with coffee filter. There's still a very light bit of grey from the old paste that I can't seem to get off.
2) Put a small dot of thermal paste on the CPU and then put the heatsink on.
3) Rotate the heatsink slightly back and forth.
4) Turn on system and watch it turn itself back off again.

Does anything about that sound wrong? I'm using Arctic Silver 5, if it matters.

This is just so frustrating because I got it to boot those two times, and now nothing. Could an improperly installed heatsink actually cause this?

Sounds like you're doing it correctly but would suggest not using a Q-tip because possible you could get a stray "fuzzy", hate to use technical terms but don't know what the cotton on the end of the Q-tip is called , but I doubt that's the problem. I suppose it possible that the CPU isn't robust enough to run that video card. Possible that you got a bad PSU. Try the PSU and video card in a computer with a more powerful CPU.

Q-tips can break & leave some cotton behind. Coffee filters are the best & cheapest. If you have airduster, blow it & let dry for a few sec, apply TIM.

I'm afraid it might be the psu or mobo.

http://www.tomshardware.com/2007/0 [...] hics_cards

There is no way he is drawing that much, and and "underpowered cpu would not cause it to not boot. If the power supply is bad, then that could easily do it.

I have never heard of that brand PSU before, how much is the PSU that your have? I've seen lot of people have big problems with cheap PSU's.

Xclio is bottom-tier PSU a.k.a garbage.

Never even heard of that PSU...

I believe the VSTA has A PCI-E slot as well as agp.