Today whilst playing CO, my GPU stalled and restored (screen went black for a few seconds) and continued playing as it did not happen.

I've had this happen before a few times and I've been wondering what could be the cause, as I'm not seeing any major performance problems when it happens and I've never had the same issue in STO?

I am running.

Windows 7 Ultimate 32-bit
Gigabyte G41M-ES2L
Pentium(R) Dual-Core E6500 2.93GHz (266.58 Drivers)
4GB Ram
NVIDIA GeForce GT 430
Realtek High Definition Audio
DirectX 11

Attach your DxDiag file and let's see what you've got.

The whole screen goes black, not merely freezes? I haven't heard of that happening before here. I used to have something like that on Civilization 4 on my old computer, and Windows gave an error message saying that the driver had crashed and then recovered, or something to that effect.

Screen goes blank, like it loses signal then comes back on.

I've attached my DxDiag

That's weird. Your hardware should be powerful enough to handle the game at moderate settings.

I'd try reseating some connections, in case something is loose. Unplug both ends of your monitor power cord, and plug them back in. Unplug the monitor cable (from both ends if possible) and plug it back in. You could try pulling the video card out of its slot and putting it back in, but that's less likely to be the problem, I think.

Okay, I'll give that a try, thanks.

Okay, whilst messing about with the graphical settings, I have found that turning Lighting Quality to "Low" completely (both in CO and STO) stabilizes the fps and stalls.

I've sent a ticket to Cryptic support in regards to this and will be asking a friend that runs a more powerful pc than me to test it too.