The first step would be to replace the CMOS battery and if the problem persists, then continue with troubleshooting. A low CMOS battery can cause problems such as the boot drive not detected among other things. The procedure for replacement can be found here. And when replacing the battery leave the battery out of the system for 15 minutes in order to reset the BIOS
Dell Optiplex 780 SFF shuts down during boot. It sometimes goes to Windows booting logo but shuts down after a second or two. It shows the CMOS battery voltage is low, I am wondering if this problem may happen because of the battery or is it something else?
Optiplex 780 SFF Shuts down during boot.