It could be clicking speeds in Windows though, so he should first check in the Windows mouse settings. Leo also suggests getting a cheap wired mouse to see if that works. Then he'll know if it's a hardware issue. If it's not hardware, then he may need to update his mouse drivers, or reinstall them. Windows may have also broken the relationship with the mouse and that could be a registry issue. Leo says to log into safe mode and see if the mouse works there.
Another good thing to try is booting to a Linux Live CD, which will let him see if the mouse works in another OS environment.
If Windows is telling him it needs to be repaired, then he'll have to put in his Windows installation disc and select 'repair from the Install menu. Another option is the Ultimate Boot CD. The chatroom recommends the Trinity Rescue Kit.