I'm having an odd issue.

Three times now my monitor (Dell Ultrasharp U2413) will go black and the power button will become unresponsive. In order to recover the situation I need to switch the monitor off at the wall then back on and everything returns to normal. Twice it's happened when I've been doing normal stuff - nothing taxing on the graphics card, mostly on the internet or desktop - hasn't happened while playing games or anything. Once it froze when I was restarting the mac (Mac Pro 3.1/Early 2008). Graphics card is a official Apple Radeon 7750 (I know it's not officially supported on the Mac but it works perfectly well).
Monitor connected by a mini-DP to DP cable (that was supplied with the display).

I recently updated to Mavericks but all the freezes occurred before that. Need to see if it happens again.

I've not noticed any screen artefacts and the graphics card fan doesn't appear to be having any issues.

So, any ideas what could be the problem here? Web search isn't terribly helpful as the vast majority of results assume you're talking about the computer freezing up not the the monitor itself.

I get somewhat similar issues with my U2413M, but that's very expressly caused by the fact that the power inlet seems to be buggered, and I have to wiggle the power cable around to get it to work again, which I guess achieves the same thing as turning off and on. The give-away though is the arcing noise it makes when you move it.

I had some weird issues with my Mac pro plugging one particular monitor into it via a display port to DVI adapter. When I just used a straight DVI cable it was fine.