Desktops forum: Desktop won't boot

Thanks, but I don't think that would work with this Pentium4 motherboard.
The docs say it only accepts memory sticks in pairs.

And that doesn't explain why I'm getting -30V or no video.

Is it possible to get incorrect POST beeps if PSU is bad?

It's a Intel D850MV:
http://www.intel.com/support/motherboards/desktop/d850mv/

And it's specifically "Three long beeps". But as I mentioned, I don't trust the POST beeps.

Would really like to know if a bad PSU can cause bad POST beeps.

for your motherboard; as quoted directly from the link:

"3 beeps - Base 64 K memory failure

Reseat the memory.
Make sure that the contacts on the memory and the socket are clean.
Try removing one bank of memory modules at a time. Note: Some systems might need to have a memory module in Bank 0.
Try using memory modules from the same manufacturer with the same part number and speed.
Check for a faulty memory module by trying the memory in a known good system.
Trying known good memory in the system.
Check the power supply and check for power fluctuations.
If the steps above do not resolve the problem, the desktop board may be defective. Try a different desktop board"

Yes, it does state that you should check your power supply, and if you really think that may be the root of your problem, then it doesn't hurt anything to buy another (reputable make) power supply to test your theory.

Pop in another PSU. There are PSU testers but for years when I head 3 beeps it was a dead board or incompatible ram or bad sockets or the chip that interfaces with the RAM (still means a dead motherboard.)

I've seen techs lose months on boards like that. I learned to get them out of the shop fast to save us from wasting hours trying to recover the dead boards.
Bob