Edit: ^ Try that first :P

Lets get a few more details.

What version of windows are you running?
Is this happening after the computer has booted up or during booting?
What is the general spec of the computer? (RAM,CPU,HDD,Graphics)

Either way, if you can not get the computer in a workable condition in Safe Mode then there is little else that can be done short of a wipe clean and re-install. If you have important files on the computer then I recommend removing the hard disk. This can be placed in a second computer to back up anything of interest. Do warn the owner of the second computer that there is a risk of a virus though.

GMAC