What i would do next is bring the pc back to a basic setup, with no peripherals whatsoever. disconnect everything except your motherboard, cpu, memory, powersupply, video card and harddrive. Try to boot with this minimalist setup, and see if the problem persists. If you don't get the error, then one of your peripherals is the problem, so reconnect them one by one, making sure the connectors are properly connected, and the appropriate drivers and motherboard settings are enabled and installed.
If the problem persists, then it is a problem with your basic hardware. I would tend to think of memory or the powersupply, but it could also be a faulty motherboard. So the next step is to try differnt memory, then powersupply, etc etc, until you find out what is bugging out.
One question - have you installed any hardware recently? Have you made any changed to your setup?
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