ok, fans means at least partial power supply as does the working video card .
a single beep at power on is significant to some bios but I dont remember the codes.

if you could get into bios you could do a manual reset but that seems not to be happening.

wiping the bios by removing the battery sounds like the way to go.

can you post make and model numbers ?

make sure you have tried a full cold start, power off the pc and unplug for a few minutes. That will cause a full cold start which a reboot from the power switch or restart from the menu does not do. 

on a dessktop I suggest removing the modem card  or other added boards to ensure its not a card failure. Not sure on a laptop if thats an option.

Single beep seems to be post test OK .