How do you get out of power saving mode?

I was wondering if someone could help me.

I was recently on a Dell computer at home when everything froze - mouse would not move on screen, pressing keys didn't do anything, etc - so I force-shut it down and restarted it.

However, upon restarting, the screen remains blank but a box comes up saying the following:

Dell U2312HM: Entering power saving mode.

For the brief 2-3 seconds this message appears, the power button on the screen shines blue, but then the box disappears and the button turns orange.

Meanwhile, the computer still starts up - I can hear the opening Windows jingle.

The screen remains blank though. If I turn the monitor off and on again, the same thing happens - you just see the message and then it goes blank again.

I've played with the buttons on the side of the monitor a bit and sometimes I get a message that says something about the computer not getting a signal from the monitor (or vice-versa, I don't remember). I've unplugged and re-plugged all the cables connecting the monitor to the computer with no result.

I've tried looking the message up online but most of the solutions I've seen require pressing certain keys (F-series buttons, etc - I've tried them all and nothing), or changing settings on the control panel - something I cannot do, obviously, without a working screen. And I don't just have a spare lying around to use.

I think it is also worth noting that I am not the system administrator (not sure how relevant that is if it is a monitor problem though).

On top of it all, I'm pretty hopeless with technical specifics with computer troubleshooting. I have no idea what is happening or why it is happening. No one in my household reset anything recently in the power options, but this is the first time this has happened, and it's rendered the computer useless.

Could someone please help me? I am at a loss.

Thank you.