There's no need to be rude, you clearly skipped the "use another machine". Use the computer your on now.

First try you monitor on another computer if it works then it is ok.
Next remove all cards and cable and make sure they are seated down.
At the same time clean out all dust from inside not forgetting the CPU heat sink and the PSU.

If it still doesn't work then try reloading windows repair first and then a full install if that doesn't work

Also, can you start it up in safe mode?

 It's not a monitor or cable issue, if it were, they wouldn't be able to see the cursor. Bacon has already explained that they don't have a Windows disc.

EDIT: Then again, it could have been a driver issue, but that shouldn't really just pop out of nowhere, unless they updated the drivers recently.

NFG, Bacon, did either of you update your drivers/do a Windows Update just before these issues started occuring?

To recap:

We continue to learn more than is ever necessary about the dynamic duo, although it is welcomed. Our main lesson of the day is learning of their ability to come to the most extreme conclusions for the simplest of problems. Our sub-lesson of the day is that they have daddy issues.

Tune in next week for more hilarious antics from our premiere Nintendo diehards.

 Rofl...This made my day.

 ye you're right.

  this is full of win.

.

seriously, they need to try logging in on safe mode. If they can do that, then they can create new files to access the net from (or possibly access the net straight from safe mode) and run the virus from there. Usually if the computer turns on and there's a problem logging in, it's limited to just those logins and it's not something wrong with the entire computer.

least in my experience.