A friend of mine has had lots of issues with his Acer Aspire 5672. When I did a system restore (restart, Alt+F10 on boot) without getting rid of the issues (keyboard and trackpad not working, general system instability), I did a bit of googling (which I should have done right away).
Turns out that the battery, for some reason, can cause these sorts of issues. My friend’s battery barely lasts a few minutes, it seems it failing can cause this – though I can’t quite see the connection.
Anyways – removing the battery, unplugging the machine, and pressing and holding the power button for one minute (which I’m guessing resets the NVRAM) magically made the machine stable and caused keyboard and trackpad to start working again. Weird. But very nice to know, if you happen to have a Acer and an issue of this kind.
I haven’t tried putting the battery back in, but I’ve a feeling that you should just get rid of it and buy a new one instead of trying to get more use out of it.
This is a funny kind of problem – I thought for the longest time that it was software-related, since the Windows installation was pretty ancient. And since they keyboard seemed to be working outside of the OS (boot menus), I thought it wasn’t a hardware problem. I guess NVRAM/PRAM issues sit right between software and hardware. Lesson learned – if something weird is going on and you can’t isolate the problem, it’s well worth trying a reset of the NVRAM.