Ok I solved this myself. I ended up trying to boot up the computer by plugging in a USB stick, a USB hard disk drive hoping the presence of an external drive would trigger something during boot. The computer still refused to get past the Boot Device LED stage in both cases. After that I booted...
Motherboard :Z97-A Asus
OS: Windows 10 64bit
Graphics Intel on board
Nvidia Dicrete GPU
The computer was working fine this morning. Shut down no problem.
In the afternoon, I replaced the CMOS battery then it cannot boot past red LED boot device stage. Needless to say I cannot get into BIOS...