Unable to boot... Winlogon error message

Hi,

I am unable to logon since this morning.

At the end of the logon sequence, at the blue screen (with the wrlcom
message), I receive this error message (this is translated from French):

winlogon.exe - application error

The instruction at "0x00000000" uses the following memory address
"0x00000000". The memory cannot be "read".

Click on OK to end the program.
Click oc Cancel to debug the program.

I tried both options, to no avail.

I repaired Win XP (rebooted via the CD rom), all the install works well,
until when the system restarts... and we're back to square one.

Any help would be much appreciated.

Thanks

Mandel