Back up his data before trying any of this!
Easiest way to fix this is to clean install of Windows.
If your friend will not go for this, you can put the hard drive in the old computer, turn it on, go to control panel and remove the chipset drivers from Programs. Once those are removed, reboot, go to device manager, make sure that the SATA, sound, video and chipset controllers have a yellow (!) on them. If not, disable them and shut the system down. Take the hard drive out, put it in new machine, boot up, see if it blue screens. If it doesn't, install new drivers and run a registry cleaner to clear out the old devices. If it does, convince him that a new Windows installation is best.