Problem logging in after failed memory upgrade

Having login issues after trying to upgrade memory 8250 Desktop. Tried to add 512 more memory to the 512 already onboard. Worked with tech support from the company I purchased the memory from and found 1 of the 2 Dimms was bad. Would get blue screen after logging in. Sometimes saw 1024 or 800mb. Reinstalled the blanks. Now I get the Windows domain login window instead of the Dell login. If I login the domain window the login process starts see the backround screen then a logging off pop up and goes back to the login screen. I did also upgrade the Bios from A01 to A04 before the upgrade. Is this a Bios issue or Corrupt Login? Update: Also tried SafeMode. Recieved the same logout. Can get to the Repair Console if I use the XP CD. What command do I run to find which file is corrupt?