Make a new user (admin account)
Restart. See if it opens ok.
If so, copy all your personal files, including your old desktop (while in new user)
Go to C:\Documents and settings\Name_of_old_user\My Documents
and copy to new user
C:\Documents and settings\Name_of_old_user\Desktop and copy to new user.
The next is ONLY if it crashes at startup!!!!,and be very carefull :
Go to Start>Run and type regedit
Click Winlogon and look to your right for "Shell"
Check if it is Explorer.exe
If not, double click Shell and write
Explorer.exe and click OK.
In the same place, look for Userinit
Double click it.Make sure it's
if not, change to that.
(if your Windows is not installed on C:\ drive , then change the letter)