Help! Seeing checker/tile boxes on boot up

I was playing a game on my PS3 last night and everything was working fine. I turned my PS3 on this morning and I'm now seeing a checker/tile screen. I know it's not my tv - because it goes away when I turn the PS3 off - but I'm not sure how to diagnose the problem to figure out how to fix it. Some people say it's YLOD symptom, others say it could be a hard drive/power supply issue.

Any help in diagnosing the problem would be greatly appreciated. The device is out of warranty, so I'm not sure how much it will cost to pay somebody to fix it, so I'm willing to do the work myself if the repair is not to risky to damaging the rest of the console. I've had it for about 3.5 years now without issue and it's never been knocked around or damaged before.