Question After unplugging all cables from my PC, my monitor is no longer receiving a signal

[Hobopotamus]

Hello,

I just installed some new LEDs to complement my PC setup, and while doing that I also completed some very needed cable management. So, I had every cable disconnected from the back of my PC.
Now, after plugging everything back in, there is no signal going to the monitor.

The monitor is displaying the "no signal" error message, so it does register that there is a cable connected to it.
I have tried replacing the DVI-D cable.

Also, I've tried opening the case and disconnecting the RAM and graphic card, as well as cleaning the whole case from dust.
I'm not sure which component could be to blame and what I should do.

Any ideas for troubleshooting?
Thank you.

Best regards,
Hobopotamus

 

[Hobopotamus]

Just to bump it and update with some more information:
There are no "error beeps" when starting up the PC. Does this suggest that it is the PSU?
Can a PSU decide to not work anymore after being unplugged for a few hours?
Thanks.