Pc not booting up anymore, need advice

Hello,

my specs: Acer Aspire M7811

CPU: Intel Core i7 860
GPU : ATI HD 7950 (aka R9 280)
Mainboard: Hard to find information about this one ( Foxconn H57.82578DC)
New Motherboard: Foxconn P55M01
RAM: 4x 2GB Kingston ValueRAM
Old PSU: FSP750-80APG
New PSU: BeQuiet! Powerzone 750W
OS: Win 7 Ultimate 64 bit


I bought this pc 2010 I believe, and I never got any problem except the GPU, that came with this pc died after 3-4 years. Replaced ATI HD 5950 with 7950 and was running like in the first day.


Last week I was playing witcher 3, when suddenly my pc screen went gray with some green lines. The background audio was looping every 3-4 seconds. I had to press the power button to shut the pc off. Since then pc would not turn on anymore.

A week before this incident I had the same problem, just randomly browsing youtube videos it just froze to this grayish screen with green lines. After turning the pc off with the power button I tried turning it on 4 times with no luck. All fans are spinning, but no beeps and not booting. Also mouse, keyboard and display not working. On the third try the pc just started normaly beeped one time and normaly booted up as always. It was working fine for a couple of days. Then it happened again. This time I resetted the bios via jumper, and pulled out CMOS battery for a couple of minutes. Tried it again, no luck. Tried again. And... pc is booting. And working absolutely fine for a whole week, before crashing again as mentioned in the first 2 sentences.

I must say I had this exact problem a year back where the pc just shut off and would not turn on for approx. 6 tries. After that there was not one single problem I had with this computer for a whole year, until recently.

I already tried my best getting it back to work, but I can't seem to figure out what the problem here is.

What I tried:

-resetting bios with jumper and CMOS battery reset >worked one time, but not anymore
-changing old CMOS battery with a new one > no luck
-trying all RAM sticks in different slots and one at a time > no luck
-replaced old PSU with new one> no luck
-using only onboard graphics on old motherboard, pulling GPU out >no luck
-bought similar motherboard on ebay and tested my components >no luck, not booting
-removed cpu cooler, cheking if processor died >CPU warming up, when turning on (seems fine)
-renewing thermal paste>no luck


The motherboard I got from ebay is not really the exact same motherboard it looks almost identical to my old motherboard, but there is no VGA or HDMI connection to the motherboard, everything else is the same.

At this point I cannot figure out what the problem might be, even after buying new parts like PSU and motherboard I still got the same problem : fans are all turning on and spinning, but pc is just not booting. There has to be something I am not getting.


I would really appreciate any more advice or pointing something out that I am missing.