My Computer has a big problem and also its a custom built pc and its always black screen nothing shows this happens in the video please watch it to the end! And it carries on till I unplug it from the power! http://youtu.be/l_4BjRCU5cI
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Seems to me your PSU may be the culprit. That beeping sounds like a voltage drop warning to me. Change the PSU and check it out. You may have damaged the GPU through under voltage as well so try swapping that out after the PSU swap.