No access to C drive

Win2k user who was able to access C drive but now cannot. This happened after I gave myself rights to be a backup operator. They get an error message that
1. They do not have permission to access c:
2. The pagefile is too small
3. The properties of ‘c’ show ‘0 used space’ and
‘0 space available.
4. A specific icon to an application is missing
5. Explorer shows ‘c’ and ‘My Documents’
I’m stuck! I have made no changes to the system other than access rights for backup. Help!!