My PC will boot, but monitor says "no signal detected"?

My PC will boot up, but my monitor will say "no signal detected". I do not believe that my GPU is dead, the cooler spins up just fine on it, and it gets warm. I have tried plugging the DVI cable directly into the motherboard to see if the BIOS had been altered but no such luck, it still said "no signal detected" which leads be to believe it hadn't. It was working completely fine, I opened up my PC (something that I do fairly often) to put in my new CPU cooler. When I tried to boot up again I ran into this issue.

Any idea?

Please help.

Thanks!

I didn't find the right solution from the Internet.

References linustechtips.com/main/topic/95824-my-pc-will-boot-but-monitor-says-no-signal-detected/

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