bob, besides checking the power supply, remember that this series has issues with a bad capacitor. "The problem is caused by NEC TOKIN 0E907 Proadlizer PF/A Capacitor for High Speed Decoupling Device, witch is responsible of coupling or decoupling the CPU hi speed/hi power(ac plugged in) or low speed/low power(ac unplugged)." Hope this helps, good luck.