Have you tried booting with only one memory stick at a time? Place the memory stick in each and every memory slot and see if you get signal on the screen in any of them. Then try with the second one.
Make sure your power connectors (CPU connector from the PSU to the motherboard, for instance) are all properly inserted.
"It keeps resetting after a short beep" -> do you get any image on the screen?
Try resetting the CMOS by disconnecting the power supply cable, removing the battery from the motherboard(located between your CPU socket and the first PCIExpress slot) and leaving your computer like that for 10 minutes, (right after you've remove the battery and the power cable from the power supply press your system's power button for 10 seconds to drain any electricity left int he capacitors) then try booting your computer without connecting the battery - see if the beeping changes. Reconnect the battery.
Check whether the GPU is properly inserted and with its PCIExpress connectors attached.
Try connecting your screen to the video output connectors on your motherboard, since you've got 3 of them VGA, DVI and HDMI - your BIOS might default to the integrated GPU instead of the dedicated one.
Try connecting power cables to nothing else but : motherboard connectors (that 8 PIN you have next to the golden heatsink near the CPU socket+ the 24PIN connector) and GPU connectors (PCIExpress). Don't connect anything else to your computer except keyboard and screen cable to the video ports. See if you get any signal.
Your CPU fan should be connected to a white connector labeled "CPU_FAN", not the black "SYS_FAN" one. Check that one out too.