Seems you have a lot of PC problems!

Try restarting the PC

Press F5 repeatedly

At the Advanced Choices Menu, try (you will have to restart numerous times to try each option):

Do Not Force Restart On System Failure

That will show you any blue screen /error message if there is one. I don't think there is though

Last Known Good Configuration

A slight possibility this might work

Enable VGA Mode

I think that will work, sounds like it could be a display issue (if the blue you are seeing is the same colour blue as the login screen)

Safe Mode

Definitely should work.

Let me know what happens with each option. If you find that Enable VGA Mode works then you should uninstall your graphics drivers from Add/Remove Programs in the Control Panel.

Also, when you do logon

Click Start > Run and type in SFC /scannow

That will scan your system files to see if anything is amiss. It requires the Windows XP CD though.

Not personally, though I know many students who do!

I appear to have rectified this problem by virus removal then running chkdsk c:/r and then sfc/scannow.