Instead of logging off, look in Task Manager and see if anything is taking 100% CPU.
Secondly, see if you have any additional startup programs in c:\Documents and Settings\\Start Menu\Programs\Start and HKCU\Software\Microsoft\Windows\CurrentVersion\Run (and RunOnce)
If all that fails, try resetting your profile - log in as an admin level user, copy your profile somewhere safe, then delete the original. Log in as yourself and copy back what you need.