PC won't boot

Hello! I've encounter a huge problem...Some days ago when I tried to start my pc and it did not boot. I've seen that after I push the power button the computer works for 6-7 seconds then it automatically restarts and continue to work, but no display. I tried to switch ram position and it didn't work. I also tried to start it without ram and it started but without any beeps. I think it could be the motherboard but I'm not sure.
Is there a way to check if my mobo still works?
Also I've had repaired my PSU 1 week before this issue.
I've also reset the bios (using the battery and the CMOS Jumper).