Frequently my late 08 uMBP freezes just from ordinary use. I have left it for a long time and it does not recover, the only way to fix it is to hold down the power button. When it resets it says that there is no airport card installed. Shutting it down does nothing to solve the lack of detectable airport card; the only way that it detects it is if you again hold down power button until it resets... however give it five minutes and it freezes again... The unibody was recently replace in a repair... what does this mean??