If you have an original graphite BS, they have been known to die with the symptoms you describe due to faulty capacitors. Apple replaced mine (out-of-warranty) with a refurbished one (still original graphite BS-not the new one) at no cost and within 18 hrs. of my calling. All I had to do was give the tech the serial number and approximate purchase date. Best damn customer service I've ever experienced from any computer company.