For the last few days, my computer has had issues booting. I've seen two different behaviors:

1. The screen displays the graphics card information, then begins to list the RAM, hard drives, etc. At different points in this process (after the graphics info), the computer shuts off. After five or six attempts, it then boots normally.

2. In roughly the same time frame, the computer freezes, and fails to boot. I think it boots successfully on the next attempt.

I've also noticed that in some instances, the computer freezes on shutdown. It gets right to the point where it should shut off, but doesn't.

I recently combined the best parts of two different machines into this one. I'm booting to GRUB, with Ubuntu 12.04, Linux Mint 11 and Windows Vista (unfortunately) as my OS options.

It has an Enermax Modu82+ 525W power supply, and I've used an online calculator to determine that my load shouldn't exceed 400W. I even unplugged a hard drive, but that didn't help.

I found the latest BIOS, patched it and checked the settings, but that didn't fix it.

I'm fairly certain this issue didn't exist at first, but might have started when the power at my new apartment dropped for a second. The machine is plugged into a surge protector strip, but it's old and I've heard they lose effectiveness with age. Is a power dip as damaging as a spike?

If something were damaged, why would it boot successfully after five or six attempts? It's almost like the BIOS or PSU need to be primed. The trouble with debugging is that there seems to be a "grace period" after shutdown where the issue doesn't present itself again.

What should I try next?