PT810 Viewsonic CRT monitor problem

I'm having a problem with my PT810 Viewsonic CRT monitor. Whenever I turn it on, and it is plugged into my video card, the monitor will make a strange buzzing noise and refuse to show anything on the monitor. The status LED is bright red when this happens and stays as such until I turn it off. If I turn it on without it being plugged into the video card or when the computer is off, it turns on like normal, though the monitor does give a no sync status.
The video card is an Nvidia 7900GT that outputs well if I plug in my brother's monitor to it. I also cannot find the documentation for the PT810 anywhere on the internet. Viewsonic doesn't seem to have it on their website. Since I got it when a software company nearby closed down, I didn't get any documentation at all. It's worked fine before this, so I don't really know what the problem is.

 

Ok, first I bought a new 15 pin cable to see if it made any difference. It didn't.
I did, however, plug the monitor into my mother's computer, which has a built in video card on the mother board, and the monitor works perfectly when I turn it on. I also plugged it into my brother's computer, which has an old 64MB GeForce 4 FX video card, and it has the same problem as when it's hooked up to my GeForce 7900GT. Thinking that it's an Nvidia card issue, I looked in their support section on Nvidia's website, but I did not find anything related to my problem

 

I can't plug the other Geforce card into my motherboard b/c my new motherboard doesn't have an AGP slot, but I did go ahead and try it again with my brother's computer, only to have the same results as when I plugged it into mine.
OK, i did get it to work... once. This only happened because I was messing around with the connection for the monitor as I turned on the monitor. I had to do this a few times, but on the 8th or so try, it turned on and displayed my desktop screen and worked normally. It did give me some wierd buzzing noises for the first minute or so that I had it on, but that went away soon enough.