I've long taken the position that if I cannot make a computer POST
in 20minutes it probably will not.... ever...
To diagnose anything you must be methodical and deliberate. to that end start by disconnecting EVERYTHING then installing only what is strictly necissary:
1)a SINGLE RAM stick
4)Monitor, preferably NOT Via a video card
The object is to eliminate as many things as possible (If you clear-cut the forest Sasquatch is a lot easier to find)
If it still doesn't POST remove the MoBo from the case
and connect everything in the "minimalistic" test setup with the MoBo resting on a non-conductive surface (cardboard works well)
And try again, if it posts the MoBo was shorting against the case.
If it doesn't it or the CPU is DEAD.,.
THAT is far as I'm willing to go on a "Zebra Hunt"
I keep a 1hour mechanical kitchen timer on my work bench for a reason.
For a Post Test on any give computer I allow 20min, if that MoBo hasn't shown SOME glimmer of life in that 20min you would hear the whistling sound it makes as it is "Frisbeed" towards the nearest trash bin. (unless under warranty in which case it goes back into the box)