Well, the last resort would be to REinstall OSX.
Yes i know this is not the result you wanted.......but it does solve many issues.
I have noticed in my 10+ year career in computer repair, that computers hat sit OFF for long periods of time suffer wierd anomolous issues.
Speculation is that condensation has set in, due to lack of air movement.
Also, computers that sit out of sight, can be prone to unknown damage. maybe a box falls onto it, or its in a box that gets dropped.
If this machine sat for a year or more, without being used, its very possible this could be the case.
Reinstalling OSX, which is a task in and of itself, will allow you to rule out a software issue, and begin to narrow in on a ardware issue.
Have you run any diagnostics on your CPU, or RAM, or MoBo?