Just in case anyone else stumbles across this thread, this was the cure for my particular frustration. I could get to the installation process, but just couldn't click the button. Infuriating.
Older build with a GA-P55A-UD3 motherboard.
So what exactly did you do to get it to work? Cause I've got exactly the same issue and it's driving me crazy since it works perfectly with Mavericks (Unibeast + Mavericks). But it wouldn't work for Yosemite. The keyboard seems to work in installer and it definitely works inside the OS itself (since I can input my password to login), if you've got enough patience to install it using only your keyboard, but the mouse doesn't. Can't click anything. There is only the pointer displayed. Oh, and funny thing, mouse-over (hovering) works as well. Just no clicks.
I would have used Unibeast + Yosemite as well, if it would work. But it doesn't. There is no Unibeast for Yosemite, for as far as I know.
I don't get it. Same USB port, same keyboard + mouse, different Mac OS X version (but I apparently am one of the very few to have this exact issue). Works in Mavericks. Doesn't work in Yosemite.
I thought it's because of the boot loader. So I tried both Clover and Chameleon. Same result. I've tried multiple IOUSBFamily and IOUSBMassStorageClass kexts. Even the ones from Mavericks. Same result.
Specs I've got:
Motherboard: GA-B85-HD3
CPU: Intel i5-4570
GPU: MSI Nvidia GTX 650 OC 2GB RAM
Mouse + Keyboard combo: Logitech LX 300
So...any idea why is this and how to fix it?