Have a Dell Studio 540 w/ Windows Vista, power supply took a dump. We replaced it and the PC worked for a couple of hours, we ran CCleaner and installed Avast. Turned it off for the night, next day when powered on it began a series of two beeps and would not boot. Reseated the memory cards, stopped the beeping but still will not boot. The power indicator light does is steady and doesn't flash/blink and is its usual color. If I press the power button withen a few seconds of turning it on it goes right down. If I wait a few minutes after powering up I have to hold the power button for a while (as if it HAS booted up). It's almost like it has lost all video output but I'm not sure. Any ideas?