Question Bootloop reason unknown

Mar 1, 2019
So its been almost 2 months that i bought a used pc from an office that closed. 250 euros with a new 22" samsung monitor and the pc with the following specs:
CPU: i5 6500
RAM:16 GB 2400MHZ(brand unknown)
MOBO: Brand unknown ru us something.
The desktop goes as HP prodesk g 403.
Everything worked fine but a wanted to upgrade with a good gpu.
So i brought a corsair tx 550m 80 plus gold. Still everything works fine.

And a week after i brought a gpu asus dual gtx 1060 6gb oc. So here we go:
Didn't fit in case so i changed case.
I plug in everything fine cause it worked but with loops in the beginning.

Last days the pc was always bootlooping and after some time it worked.Keep in mind that i was able to play. Apex/BFV/BF1 all on high 60fps at least.
Yesterday though it "died" i unplugged everything reset cmos but still bootloops. No bios no nothing, pc boots for 3 seconds shuts down and restarts.
The only way it works is i remove the ram sticks.But ram sticks are not faulty guys since i tried them to my friends pc. I plug hes then in my pc still nothing. Its something about the slots maybe????
Maybe its motherboard faulty??? All fans everthing works fine. And yes when i have the ram sticks unplug it flashes the red light.( no beepings though)

Thank you and sorry for read-marathon.
Any suggestions welcome since im looking for help.
And im in tight budget to get new mobo if needed im thinking of ASROCK B250M PRO4 RETAIL 80 euros.