XP- Logon immediate Logoff problem

I have never encountered this one before ... I just reinstalled my XP Pro OS and was well on the way to reinstalling all my programs and updates when suddenly I tried to login after a reboot...I got a flash then the "ctl-alt-del" login window pops up again.
This is on a 1 ghz AMD Athlon with 512 mg memory - XP SP2 machine
Reason for the reinstall was some hacker hijacked my Administrator access rights so that I could not make any changes or update my virus program or firewall. Not finding a way to get my access back, I wiped the drive and reinstalled.
The problem happened after I had tried to load Nero Burning software that failed on the install, so I installed Roxio EZ CD Creator. Also the Nero program would not uninstall.
Any ideas on the cause or if there was an easier fix than reinstall with repair.
Thanks .. Don

 

My first guess would be after you installed windows, you reset the date and time, then your 30 day unlock time was gone.

 

That would be it! noticed the date was off by a couple months so I reset it. I just didn't make the connection to the activation..
Thank you for the prompt answer.
Dheitt