Try starting over. Put the motherboard with CPU+HSF and PSU on cardboard and re-test. It should beep in protest of no RAM and GPU. At that point you can check there are no extra mounting studs in the case and see if it beeps in protest in the case (again, only need the MB+CPU+HSF and PSU.
Add a piece one by one till you find Waldo.
Today I upgraded my pc hardware. I installed new psu (Corsair vs550), motherboard (asrock 890gm pro3), cpu (phenom ii x6 1100t), gpu (gtx 660) and new ddr3 ram. I had some trouble with the wires but I managed to install them. Everything booted up fine, upgraded bios and drivers. (there was somekind of error in mobo drivers) Started playing and in the middle of the game computer freezes to black screen and i had to reboot. (temperatures were good) When i tried to reboot only psu, cd drives and hdd seemed to work. There was a light on the gpu but even the fans didnt work. I then switched ram slots and when tried to boot everything seemed to work fine but there was still a black screen. Later all the fans stopped working again. Any suggestions what would be the problem?