Memtest86 Advice- Weird stuff

Alright, yesterday I upgraded to an 8800 GTS, because I had a strong suspicion that my graphics card (old one) was performing badly and overheating, which was causing black-screen game crashes.

In all games except for one this stopped my crashes. This time, I experienced a screen freeze with repeating sound. I am not sure if this is a game bug (it's in beta) or an actual problem with my machine.

So I decided to run Memtest overnight to make sure everything is working. I ran memtest, and then turned off my monitor so my screen wouldn't be damaged.

Today when I turned th emonitor back on, the monitor says it's getting a signal, but that signal is just a black screen. What does this mean? Is this normal for Memtest? Did my graphics card decide that it was done displaying the memtest bluescreen? Is this indicative of an error, or is this just what happens when memtest gets bored, or the graphics card goes into some kind of hardware induced sleep mode after not having a monitor to connect to for 8 hours?

Either way, the frustrating thing is that I never got to see the memtest. I am restarting it now, but I am worried I'll encounter the same problem while I'm not looking, since I have no intention of leaving my monitor on displaying that brilliant burn-your-screen-out blue for 8 hours.