Question HP Compaq Elite 8300 Turns on then turns off right away. Blank screen, No POST, Green led on, Fan spins

[smockus]

Hi all
I have a HP Compaq 8300 mobo I got from ebay. But I have no display or POST, green led, CPU Fan spins and shuts down right away.
CPU is an i7. The PSU is a 6+4 connector and not 20 pin
Have done all the usual troubleshooting:

• all cables connected, aux led is green, no blinking
• when I press the power button the power led turns green (no blinking) and the fans starts
• no beep, no red led, no blinking, but nothing happens on the display (connected via VGA)
• after a few seconds, it shuts down

I tried the following:

• remove dust with a vacuum cleaner
• reseat ram
• leave just one memory stick
• reseat CPU
• reset CMOS
• replace the CMOS battery
• disconnect everything non-essential
• remove all ram sticks, tried different combinations

-tested the power supply with a PSU meter.

So now, I'm stumped and frustrated because I've been working on this way too long. HELP!!

 

[Fix_that_Glitch]

I would look the motherboard over closely and check for burnt, melted soldering, bulging, melted transistors, paying close attention to the area around the front and back of the cpu socket.