Single Player won't Start

This is not specifically MY problem, but for my bro. His garry’s Mod won’t allow him to start Single Player. When he clicks on it, it acts as though he never clicked it, except for the animation that appears when clicking it. The same goes for when he clicks Garry’s Mod settings. Can anybody help him out here?

A few people are having this problem.

See: http://www.facepunch.com/showthread.php?t=891988

Yeah, i saw that thread. I think it’s all due to the OS.

It’s not the OS…

It’s a fucked up gmod update.

its the fact that you have x64 bit OS