Problems logging into Windows XP?

When I try to log into my Windows XP User Profile, it comes up with an error message saying it can't log me into my profile, and it logs me into a default profile. The detail part says there is insufficient system resources. It has happened before but normally if I just restart the computer, that fixes it. This time, its lasted several days. Every time I log in, the same message comes up. I've run several virus scans and it still hasn't changed. I also can't use Live Messenger, but I don't know if thats related or not.
There's still like 20GB left on the hard drive.

Insufficient hard drive resources makes me think that that your hard drive is running out of space. Open My computer, and right click on "C:" and select "properties". If you have less than 1 Gb (1000 mb) then you should uninstall some programs to free up space.