im thinking its one of three things...
1. sound card is failing. this could account for the clicking you hear in your headphones. if it is an integrated sound card, that leads us into possible problem 2. (please let us know if its integrated or not)
2. motherboard is failing. again, this could account for the clicking in your headphones, even more so if you have integrated audio.
3. power supply failing. could account for the screen going blank. (i personally believe this one is the least likely, but it is the easiest one to troubleshoot.)
i would use a PSU with the same or higher wattage rating then the one you currently have and see if the problem continues. if the problem persists, then it is not the PSU's fault. if you have a sound card, pull it out and see if the problem persists. we will delve more into details if neither the power supply or sound card are to blame.