You have done good job trying to resolve the issue. That short beep is different from the normal post code, right? Is it a bit longer? If not, and you suspect that it could be the post code, the problem may be related to the video card. Are you using a dedicated one? Please remove all, but one stick of RAM. Keep the PSU cables only on the motherboard and the video (if you have one). Try to boot. Does the same sound appear?
Hope this helps