Can no longer access C drive

Until last night W7 was working very well for me.
Now I can no longer access my C drive, Get a message that the administrator (me) has banned me!
At the same time, I started gettin a message that my antivirus key is not valid.
Antivirus no longer works. (Avast).
Also at about the same time my email programme (Thunderbird) started telling me that it could not download any more messages as there was insufficient room. Even after deleting several messages, the same fault continues.
It looks like scrap W7 and reinstall, unless anyone has a better idea.

Advice would be gratefully received.

It could be that your have been infected with a virus - as it doesn't seem right that your AV software has stopped working or that you can't access your main drive.

I'd opt for a full re-install to be honest as that sounds like a complex series of issues that would be very difficult to troubleshoot.

Hey ya, Ian is right, that sounds like a bad virus you have there. What you could do is, insert the R/C disk and boot off it. You can now try to repair it via several was...
By the way does it stop you before or after the windows boot animation?
Pictures?

Did you join/create a HOMEGORUP ??

Seems there is a bug in homegroups whereby permissions are changed.

I did, and lost full access to C: - had to run MMC.EXE in Safe-Mode to recover the permissions.

Here's a link to the MS forum explaining it a bit better:

http://social.technet.microsoft.com/...4-13ccceeb756c

Yes I did. Thank you for the advice. Unfortunately by the time I received it , I'd already scrapped and reinstalled W7. What a job. This could probably have saved me a lot of heartache.
Thanks anyway, I'll know for if it happens again