computer only responds to power button
I was setting back up a computer that had been sitting in my closet for around a year and a half. However, when it turns on, there is no video signal, not even for the BIOS. The only signs that the computer is on are the fans (including the one on the video card), the power LED, and the scroll/caps/num lock LEDs on the keyboard flashing once at startup. I have tried two video cards and two CMOS batteries, so those are not the problem. I have unplugged everything except the motherboard with the same results. It seems like something went wrong with the BIOS while sitting in my closet, but Ionno how I could install a BIOS update or manipulate it in any way with the system in this state.
The computer worked fine before.