Bah! I had typed up this long explanation of what the problem is, only to be bamboozled by using your "manage attachments" 'page'! Using Firefox, it opens the "manage attachments" in the same window as the reply - and I can't "close" the window, nor can I go back a page to post it!
To cut a long story short, I did got a BSOD later on - after I first put the new RAM in correctly (which is included in this post - using IE 9 this time!). I didn't think it was related at first, but now I get the feeling it might be.
I've got two GeForce 8800GTS' via SLi. When I plug my monitor in the bottom card, it works (but it says it's not attached to an NVIDIA GPU, and there's no Aero etc. - although I can up the res to 1280x1024, so it's not like SafeMode in that respect), but when I plug it in to my top card - the one I've always used - the monitor doesn't come on.
So does that mean my graphics card has died? It can't really be dislodged, as both cards are physically fixed together by that bar which allows the SLi thing to work, I guess.
*edit* I've also got a "Code: 43" for my graphics card, and a "Code: 28" under 3D Video Controller in the Device Manager.