Macbook (white) grey screen

Hi there guys this is my first time on this forum just trying t find out some information about what happened to my macbook

heres the stats on what it exactly is.

snow leopard
2.4GHz intel core 2 duo
2GB RAM
160GB HD

I purchased it this time in 2008 from my local mac store. never had a problem at all until last night. I was watching a youtube video and suddenly it beach balled and wouldn't do anything, so i held the power button down and turned it off and back on. After turning it back on it wouldn't do anything except stay on the grey screen with the apple logo.

I reset the PRAM, did nothing. I booted via the installation disk, verified and repaired the HD, did nothing, said the HD was working fine. No problems.

So after all, I archived and installed the original leopard. obviously keeping the previous system, and everything seems to be working fine ( for the moment )

I personally can't really think what the problem could be except from maybe snow leopard? but i've had it on for about 2/3 month so.

But yeah, just wondered if anyone had any information or guesses on what the problem could be.

Thanks guys

Sam