So I was troubleshooting a computer today and I am totally stumped. Computer has not been turned on for about 18 months but worked prior. Upon first boot, computer could not find boot option for Windows. Hotkey to boot menu did nothing. Only F key that worked was the one to go to the BIOS. Looking in the BIOS, nothing interesting. Boot order looks fine. Upon reboot, the system spontaneously reboots after 5 seconds repeatedly. Code 24 is the code on the mobo LED when it shuts down.
Pulling power cable or switching off PSU so that power can drain (no need to pull CMOS battery) results in system again being able to boot back into BIOS setup. But again, after any changes, continual reboots at code 24.
Pulled RAM and tested fine. Pulled CMOS battery and replaced. Pulled video card and replaced. Nothing changes behavior.