The computer's CPU turns on, but the monitor does not.

I have a very old computer, my problem is the following: the CPU turns on normally, but the monitor doesn't. I couldn't identify the CPU model, but the monitor is an LG Flatiron W2252TQ-PF, manufactured in 2009. This happened suddenly. I turned it on normally, and it worked normally, I turned it off after finishing using it, and when I went to turn it on again, this happened.

The monitor is not completely inactive, it turns on for a moment (separately from the CPU), gives a signal (digital: power management) and turns off again, someone said it wasn't going through POST correctly, but the monitor is not even turning on. There is no sign of physical damage, I think it's something to do with the connection. I disconnected ALL cables and connections, cleaned everything, connected it again, but it didn't work.

And an addendum, this computer was at my grandmother's house, when I brought it to my house for the first time, it worked normally, so I don't think it's something related to voltage difference. It really was something sudden. I hope the details provided are sufficient, thank you in advance to anyone who helps me!