I have two displays and I want to run my virtual machine on both displays in a Full Screen mode.
If I go to View menu (in the Mac OS X menu bar) option 'Use all displays in Full screen' is gray and unavailable.
There is no 'Display Adapters' in Device Manager (go to Start > right-click on Computer > Manage > Device Manager) and the proper drivers for Parallels Video Adapter are not installed.
NOTE: We recommend you to take a snapshot before proceeding with further steps. To create snapshot please follow: Working with snapshots
After snapshot is created, please continue with the following:
Go to Start > Control Panel > Display
Open Settings > Advanced > Adapter
Check what video adapter is listed there (in this case it was VGA device)
Click Properties and choose Resources
Check the field: 'Conflicting device list' (e.g. "Intel(R) 82815 Processor to AGP Controller - 1131")
Go to Device Manager. Find conflicting device in the list (e.g "Intel(R) 82815 Processor to AGP Controller - 1131") and choose Uninstall
Right-click on Computer (at the top of the list) -> Scan for hardware changes.
Wait until Parallels Video Adapter is installed.
Restart the virtual machine.
Enter Full Screen mode.