Not sure whether your issue has been resolved or not but I'd ask did you install any new hardware or software? If booting it with safe mode does not work than some servicing may need to be done, including re-seating the fan connection, replacing said fan, cleaning all the cooling fins, inside and out, and if you really want to, you can take the cooling system out, clean all the old thermal paste off and plop some fresh new thermal compound in there.
Put it back together and you should be okay!