It really doesn't have a simple cause or cure but many. Google The Dead PC and you see the usual ideas.
You get to try cheap to more expensive part swaps until you find what it is this time. I always start with free ideas like remove any part that is not needed to get a beep or display then cheap like a new CMOS battery then another video card unless it's onboard and then we are looking at power supplies, motherboards, etc.
I have an old Gateway desktop. The fans turn on but it won't display anything to the monitor. I reset the CMOS and nothing happened (still). When I removed the RAM cards the computer makes one beep, but still does not display anything to the monitor. Any help is appreciated!

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