Just as topic say. i play for 45mi to and hour, 3 hours being the longest and then my monitor goes into powersave mode and wont go back on when i turn it off and back on with the power button. any ideas what is causing this and what to do to fix this?

I'm having the same problem. I'm relieved that its not just me though. Anyone have any ideas?

Consider that your graphics card may be overheating. I had this problem with my older card. There are places in the game that, for reasons unknown, can really cause heat spikes.

You could be right. I updated my drivers the other day and it would appear that it shut off SLI. So its been running with 1 card. My settings were probably too high for 1 card. I switched SLI back on and I'll let you guys know if it helped. Not sure if this is what caused it for the OP though...

You might also try a video setting in the ingame options menu.

Video -> Troubleshooting (this is a tab you may need to click on at the bottom of the Video page) -> Reduce CPU/GPU usage.

It says it can help with overheating issues, at the potential cost of performance. There is also a
'GPU-accelerated particles' option. If it is an issue with your GPU, maybe disable this, so that it makes the CPU take over this work.

You can also boost the video memory limit here too (card memory iirc).

This is also related to lag : I had the same issue ( monitor momentarily stating there was "no signal " from the graphics card ) after seeing "server not responding " for about 25-30 seconds and immediately worried it was the GPU .There wasn't anything wrong with it though , temperature was just fine .

So if you see this when also experiencing server issues it could be that is the culprit ( check GPU temps just to make sure though )