Hello,I have a problem with my local disk:c/ actually,I went to poperties of local disk c.I edit the permission and click deny box. I just click it, I did not know what the function of it. And then my local disk c cannot open. Can somebody help me, now I know what the function deny or allow. But now I cannot return it to normal back... I try many ways.. but...

You'll need to log in, via safe mode, into the primary admin account and UNdeny access, that's assuming you didn't change it to deny everyone.
If that's what you have done then the only sure fire way for recovery is a rebuild.

The deny permission is EXTREMELY powerful and should only be used as a last resort.