This does not appear to be a problem with the graphics card. It's likely that Windows 7 is not properly detecting your monitor, so try this:
1) Click Start
2) Right-click "Computer", then select Properties
3) Click "Device Manager" (you may need to respond to a UAC Prompt
4) Under "Monitors", right-click you monitor, then select "Uninstall"
5) confirm the device removal
6) Have Windows re-detect you monitor by clicking the "Scan for New Hardware" button
If the above fails to work, then you might have better luck if you go to your Monitor manufacturer website to see if you can find the drive (usually some kind of INF file) that tell Windows what the capabilities of the monitor are, including refresh rates and screen resolutions.