Just this week I've started to experience an issue with my mid-2009 15" MacBook Pro. I'll be working along and suddenly everything will freeze. About 10 seconds will go by and then the computer will restart itself. When it comes back the wifi icon doesn't look normal and if I click it it says "no wifi hardware installed". If I shut the computer completely down and turn it back on, everything comes back normal. This has happened 3 times this week. Any idea what's going on? I'm running Yosemite 10.10.2 with all of the latest updates.