Please Help!

Windows XP Professional Service Pack 2.
An unknown user account (named mjRjnWcQcq) has appeared on my laptop.

I can delete the folder c:\Documents and Settings\mjRjnWcQcq and registry values containing mjRjnWcQcq.

When I reboot, mjRjnWcQcq is back!

I am unable to switch to another user or login as Administrator.
Control Panel User Account options seem to have been disabled also.
I've ran numerous anti- virus, spyware, trojan, etc programs and cleaned the laptop of all detected problems.

mjRjnWcQcq remains undetected (whatever it is).
How can I get rid of it?

I couldn't find any reference to that account name. Some programs (like backup utilities) may create a user account to perform some function. Delete the account and boot to Safe Mode to see if its recreated.

Thanks ScottGem.
I yried your suggestion.
The account is not there in safe mode.
But it came back after a reboot.

Ok, that's good. That means something is creating the account when you boot normally. Go to Start>Run and type MSConfig. In the Startup tab, see if you can find anything you don't recognize and uncheck it. Then delete the user and reboot and see if it comes back. If it doesn't that its one of the things you unchecked.

Unchecked a few items, deleted the account, but it came back after reboot.

You are going to have dig a bit to find out what it creating the account. Maybe uncheck EVERYTHING and then recheck items 1 by 1 to find the culprit.

After poking around a bit, I've managed to screw up my desktop.
Now after a re-boot my desktop settings appear to be some default where none of my toolbars or shortcuts are visible. I have to set up my toolbars/shortcuts, but the next re-boot reverts to the default and my changes are lost.
I'm considering a system restore...
Thanks for your advice ScottGem.

Sounds like one of the things you unchecked was your video adapters control program. Try rechecking that. Look for something that refers to NVidia or ATI.

If not, do a System Restore.