MacBook freezes on gray screen and does not start

Hello, this is my first post and I will really appreciate if you could help me. Yesterday I started my macbook and it froze on the gray screen with the withe apple. I restarted but nothing happened. I left it all night until the battery went down. Nothing. The only thing I could think of is the following: I found out that most of my HD was full (120 GB) whihc was a surprise to me, and I started deleting unnecesary files. So, either I erase the wrong file (though it worked fine and I did not delete system files) or I have a virus...
Does anybody know what to do?

sebacuret,

I don't think it's a virus, Macs don't get them, but you could have deleted a significant file required for running O X.

Try starting in the Safe Mode (install disk, hold down S key) and if that doesn't work, try it again and hold down the C key and go to Disk Utility. If you get there, run Verify Disc and check results. Then if it comes up, use Repair Disc.

If none of that works, you may need to re-install. Do you have backup? If so, erase your hard drive from Disk Utility and restore the backup. Might be a good time to replace the hard drive before you restore the hard drive...

Maybe someone else on here will have a better answer...

Good luck, Noel