Question How can I fix my old 3rd gen system?

Jun 5, 2020
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So to give some background. Got the system from a hotel I worked at for a while and thought it would be useful as a sleeper pc to run monitoring software on while my main pc is off.

The Problem is that it won't display anything on any monitor with any connection. The system posts with no beep codes but the display remains off.

Specs: i3 3120
Motherboard: No idea, some old green 3rd gen
Ram: 2x2gb DDR3 1866mhz

The PC worked for about 3 months and now is dead. The PC used to have this weird thing where you have to have an old Microsoft keyboard plugged in to boot it, otherwise it would give a keyboard error.
So I've tried everything I know how to do, the motherboard lights come on and the CPU cooler ramps up in speed then drops to like 30%, which is what it does when it boots. But still no display. I've tried a different PSU and made sure it wasn't that, then I tried resetting CMOS and removing ram. Pc gives the correct beep codes when no ram is inserted and no CMOS battery in. I've tried just one stock of ram in both slots and tried the other stick in both slots, I've also tried putting my GTX 1080 in from my main pc and still the same thing, I've tried 4 different monitors already with, display port then HDMI, then DVI then VGA, and still no boot. I've re-seated the CPU and gently straightend the only slightly bent pin.

I just don't know what to do, could you guys please help me.