WinXP : no logon

ok, I have had several units in the past few weeks, all exhibiting the same problem. I was wondering if anyone else has seen this or know how to fix it.

The cpu gets to the WinXP Welcome screen and freezes. I have tried safe mode, last known good settings, chkdsk, etc. to no avail. Actually, when you try to boot into safe mode or last known good settings, it stops at the same point. The mouse and keyboard are functioning but Windows will not go into the desktop.

This has been different brands both new and used CPUs, all hvae been running WinXP Home (not sure about service pack status).

The only thing I haven't thought about trying up to now is to pull the hard drive and scan it for any virii on my bench computer.

Any Ideas ??

When booting to safe mode - does it complete the list of files and begin with the desktop? Or does it stop at a certain file?

If it does get to the screen, what happens when you press crtl alt del?

Booting into safe mode: Yes it does go trhough the file list as the OS loads. Gets to the welcome screen and stops. does not show user accounts (e.g. administrator) CTRL-ALT-DEL does nothing.... does not come up with task manager.

It should come up with the login screen, try pressing ctrl alt del twice in rapid succession.