Windows 7 Keyboard Issue - Windows 7

A friend of mine has a custom built desktop that runs Windows 7 Ultimate Service Pack 1. The keyboard doesn't type "s". It will type Capital S if I press "Shft+S" but not Capital S if I have caps lock on. "Windows+s" results in "s" and keyboardtest.com registers the keyboard hitting the S key. sfc /scannow results in no registry errors, reinstalling keyboard driver doesn't work, reverting to a more basic Microsoft Driver doesn't fix it, changing to a custom keyboard layout has no effect, and the weirdest thing is that it works in Safe Mode. Keyboard is totally fine. Works perfectly in another computer. No viruses or odd programmes installed. The logical point of action here is to reinstall Windows, but that's a no-go at the moment. Need a quick fix. Any recommendations or experience with this?
Thanks!