SymptomsWhen you enter Full Screen mode in Parallels Desktop 7, Windows (or whichever guest OS you're using) expands to fill one display, but any additional displays connected to your Mac are unusable.
By default, Mac OS X Lion allows you to use only one display in Full Screen mode.
Resolution1. Stop Windows or whichever guest OS you're using.
2. Update Parallels Desktop to the latest version (build 14922 or later): In Parallels Desktop choose Parallels Desktop --> Check for Updates. Then follow the onscreen instructions.
3. Once the update is finished, choose Virtual Machine --> Configure and click Options.
4. Click Full Screen and deselect Use Mac OS X Full Screen.
Now when you enter Full Screen mode in Parallels Desktop, you can continue using additional displays connected to your Mac.