From time to time coherence mode seems to play up on some Mac’s. This is what we normally do if Enter Coherence is greyed out in Parallels 10 when Windows 8 or Windows 8.1 is the virtual machine.

Step 1. Open the Device Manager

Windows 8 – Move your mouse to the bottom left hand corner and right click

Windows 8.1 – Right Click on the Windows Icon at the bottom left hand corner

Step 2. Uninstall the Parallels Display Adapter

1. Select System from the menu that appears
2. Choose Device Manager from the System Windows that pops up (left hand side)
3. Expand Display adapters
4. Right click on Parallels Display Adapter (WDDM) and choose uninstall
5. Put a tick in the checkbox which says “Delete the driver software for this device” and click ok.

Step 3. Restart Windows

Step 4. Reinstall Parallels Tools

1. When windows restarts click on Actions from the top menu bar on your mac
2. Click on Reinstall Parallels Tools

Step 5. Restart Windows

Check to see if you can now enter coherence.