User profile defaults to "temp" on reboot

MRL325i

Hello. I am using Vista basic on a Dell Inspiron E1505 laptop. Just
recently, when the machine is rebooted, I get an error message that the user
profile is not loading correctly and the pc goes into a routine where it
boots up to what looks like the default setup -- it says that it is creating
a desktop, and all of the Dell support stuff pops up. I have to do the
following to get back to my original setup:
go to command prompt and enter "set userprofile=c:\users\PROFILE NAME and I
have to shut down windows explorer and then start it again after I have reset
the userprofile.

Why is this happening? My antivirus stuff is up to date. Thanks.