well this is my guess. i know that a low cmos battery can cause all kinds of problems with forgetting settings etc which can sometimes upset the boot process. However, not switching on at all is a little unusual.

Next...is there something shorting on the mboard...nothing obvious...how the hell can you find it if it has been scratched in any way...by perhaps a slipped screwdriver in the hands of a lunatic.

finally i notice that the metal surround is missing from the 2 onboard usb ports at the rear. If this has been removed/lost then i think there is a possibility that it may be causing a short or even not making a contact that it should be and perhaps a circuit is either incomplete or damaged through a voltage change.