From what I see the optimal resolution of your monitor is 1440x900 and if it worked before …

Check that the cables are properly plugged in and try booting with a LiveCD to see if it lets you configure to the native. In the NVIDIA panel, look to see what parameters you can change and try. You shouldn't have problems with the refresh rate but make sure it's 60Hz and that it doesn't force any horizontal refresh or anything like that.

You can try installing drivers specific to your monitor. If there are none for Win7, try the ones for Vista.