Helping a neighbor with her laptop, was running fine, then wouldn't boot. It is a HP Probook 6550b. When I push the power button, I hear a fan for about 10 seconds, and 3 lights, then nothing. I have tried a hard reset (removing battery and power cord, pushing power button for 15 sec, then reinstalling battery & power cord and attempting to start.) I have also put a win 7 disc in the cd drive, as well as a win 7 USB thumbdrive, no change. any suggestions? or is this laptop toast?