[Timeless Enigma]

So, I've got a problem, and it's really just manifested itself in the last few months, I've had the computer since November with no real problems.

The basics are I can no longer consistently boot my PC successfully.

Key symptoms:
- PC freezes during boot up screen (during POST)
- if PC gets past POST, sometimes it will freeze during the Windows XP loading screen, or some time shortly after boot up... or... long after a boot (hours later or days later)
- HDD access light (I assume that's what it is) stops blinking whenever this freeze occurs
- sometimes PC doesn't even beep once after powering on (and no video is displayed on monitor)

Basically my only solution has been to just not shutdown my computer, but then my landlady complains about me using too much power. Hibernation or Standby doesn't help, I always have to boot from scratch.

When this problem first started, it used to just be the rare freeze during a normal PC session (usually accompanied by a kind of blurred video signal), and then I'd just reboot and everything would be fine. Then sometimes, out of the blue I would stop receiving a video signal. At first I thought this was a video card/cable problem.

What I have tried
- First assuming it was a video problem (my PC has onboard video) I bought an external GPU, no improvement all.
- Someone recommended I up the PSU, because I was using a stock computer (it was originally 350 W) and I had 3 more HDDs and 2 PCI devices added.
- I replaced my PSU with a 500 W PSU but no real improvements

I guess what's left now are RAM, CPU, or motherboard but I'd like to hear some advice as I can't really spend money to replace these things just yet.