If you already tried degauss, it probably is dying.

> However, I have noticed that:
> --If I turn the computer on for a while in the morning, turn it off, and then
> come back in the afternoon it works as normal...
> --By shutting down the computer and then taking the lead out of the back of my
> video card and plugging it back in seems to make the monitor work as normal,
> until turning it off and coming back the next day... then the problem returns...

:/ Sounds like it might be dying.

> Just wondering if what you guys think. Is it the monitor as I suspect, or maybe
> some interference (though nothing on my computer has changed, nor has it been
> moved since this started happening), or could it even be my video card?

Yeah, there's a chance it could be some parts on your video card associated with the RAMDAC (converts the video card's signal to output to your monitor) might be dodgy, and are acting up after a while? But I don't know how you'd detect or fix that so easily. You could always try it on another monitor, or try something else on the monitor you have now.