I have found some threads describing this problem on Google, but none of them provided an (working) answer.
I have installed beta of Yosemite on my MBA (2013). I made no back-ups, but it's my secondary computer and I have no important data here. The problem is: internal trackpad and keyboard stopped working suddenly - during internet browsing on Safari. What's more, mac was running pretty slow during the first hours after the problem occured. Then, this issue fixed itself.
When I connect mouse and keyboard via USB - it' all OK. What I already did:
-checked all what I could in system settings UI
-Reinstalling OS X
-Hard reset (erased disc) to factory settings with Maverics OS.
However, it should not be a hardware problem - I can enter recovery mode ( Cmd + R ) with my internal keyboard.
Does someone has any more suggestions ?