Suddenly Windows XP Cannot logon

Viruses and worms
1

I left this machine out for lunch, when try to logon got this message:
“The system cannot log you on due to the following error
The parameter is incorrect
Please try again or consult your system administrator”

When i used the wrong password the machine knows
"Did you forget your password?
Please type your password again "

Also happened in safe mode. Any idea what is toasting this machine?

Machine spec
PIII NB, Windows XP, AVG 6.0, ad aware,

Happened to every account in this machine

2

Try the administrator account.

And out of curiousity. Why asking here while you use AVG?

ps: Questions like this should be in the General Topic forum or the Off-Topic forum.