Odd XP problem. Users deleted, control+alt+delete not working

[jimmyrules712]

In my office there are 2 computers that within a couple days of each other (it may have been the same day) the main users account was somehow deleted from the computer (they couldn't log in the next day and I had to re-add their account).

Then I noticed that on both of those computers control+alt+delete doesn't do anything anymore expect a brief flash. I'm not sure if that started happening the same day as the above issue but it's very possible.

I did some googling and saw the possibility of a virus but both computers have the most updated Trend-Micro installion running and it's never detected anything and I know at least 1 of the users has never been the kind of person who had issues with getting viruses.

I'm also confident that the computers were not victims to intruders with physical access to the machines.

Ideas?

[shadowpr]

I would try to scan the computers with a different anti-virus just to eliminate that as a possibility.

[jimmyrules712]

I just scanned them all this morning and nothing shows up so I'm pretty sure it isn't related to a virus, or if it is it is something the anti-viruses can't pick up. All of the affected computers have been reformatted within the last 6 months and none have typical viruses/spyware symptoms like poor performance.

From what I can tell it the problem started on 3 of our computers all on the same evening.