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#51
Strip your system down to the bear essentials. That means removing all add-in cards, peripherals (such as HDDs/SDDs/optical drives - disconnect the data cables and power cables) and all but one stick of RAM (plug this into the socket nearest the CPU). Make sure that the PSU is connected correctly to the motherboard and that ther CPU fan is plugged into the correct motherboard header - refer to the manual. Power up. Do you get a display? If all is well, you should get as far as the missing OS message. If not, try a different stick of RAM. If you still don't get anything after trying all memory modules, repeat but this time in a different socket. Next, start adding components one at a time. I would start by adding the RAM. Remember to disconnect from the mains whilst removing/fitting components. If all goes well, you can add in the drives, again one at a time. Testing is done in two stages here - the first with just the power connected to the peripheral and the second with the data cable as well. The reason for this is to eliminate any possible internal fault with the interface circuitry on the device itself. If any of the drives is/are PATA as opposed to SATA, make sure that the jumpers are set correctly (I don't recommend the CS setting, instead manually setting them to MA and SL for the master and slave device respectively) and that you are plugging them into the correct location on the data cable. When you get to the point where your system fails to boot up, check by back-tracking and disconnect the last thing you connected.
Hope this helps. I realise that this will take time, but it's best to do things like this slowly and methodically. We'll be waiting for you.