O.k. I reinstalled Windows and there was no errors! however, after I installed AVG 2011, the corruption errors re appeared again! So I uninstalled AVG and I ran chkdsk and the errors dissapeared! So I guess my problems were all caused by AVG Free edition!
I'll still run chkdsk to make sure that the errors are gone...
So, now I'm stuck with a new problem: Should I download the newer version of AVG Free 2011 or look for another trustworthy anivirus/antimalware/antieverything program.
(I would like to have some sort of real-time protection to stop attacks in their tracks too.)
After 2 weeks or repairing and testing, I found the problem! My HDD. So I put in a newer 80GB drive and it works.
Thanks to everyone who helped!
P.S: If anyone uses chkdsk and it says something about "Fixing errors in the volume bitmap", ignore it as I found out that the chkdsk utility can report false errors sometimes. Only trust chkdsk when you are useing the chkdsk/r option!!