Two things:
1) nothing changes on it's own. Your friend installed "something".
2) Windows has problems writing to or deleting files that are in use, such as video drivers. The best way to solve problems like this is to boot to safe mode, and *then* remove the item from device manager. Windows loads it's own, basic drivers in safe mode, allowing you to get rid of and clean out the old, "real" drivers. You'll be surprised how often you see double items (such as two monitors or screen cards) in safe mood, because all the "half" or failed installations show up. Remove them all, and let windows find the item again on reboot, then install the drivers.
If your confident enough, it's also worth searching through the registry and removing any references to the hardware in question whilst you're in safe mode. A word of warning though, screwing up the registry will mean a full system re-install, so make a back up, and make sure you know how to use the backed up registry files.
