Please follow the instructions from this article:
111474 Unable to switch to Coherence mode
Video driver issue
Go to Start > Control Panel > Add/Remove Programs (Programs and Features) and uninstall Parallels Tools. Then click on the Virtual Machine option in the top Mac menubar and select Install Parallels Tools.
Go to Start and right-click on (My) Computer and click on Device Manager. Check if the Video Controller is successfully installed. If it's in yellow, that means that it was not installed properly:
Right-click on Video Controller and choose Uninstall. Then go to Action and select Scan for Hardware Changes. Follow the on-screen wizard to complete the installation.
Optimizing virtual video performance
Shutdown your virtual machine. Click on the Virtual Machine menu in the top Mac menubar, select Configure > Hardware > Video and make sure that both options Enable 3D acceleration and Enable vertical synchronization are checked.
Set the amount of video according to the Windows applications' requirements (e.g. in case you use graphic applications which require high video memory, set in in accordance with system requirements). Set the amount of video memory to 256 in case you do not use any particular graphical applications.
Go to Start > Run and type dxdiag command there. It will open the window where you will see the type of the driver installed and if 3D acceleration is enabled:
Issues with dynamic screen resolution
Please follow these steps if you are unable to resize the Windows window:
Click on Devices option in top Mac menubar, choose Devices > Keyboard > CTRL+ALT+DEL and click on Task Manager.
Switch to Process tab.
Check if prl_tools.exe is running
If this process isn't there, go to Start > Control Panel > Add/Remove Programs (Programs and Features) and uninstall Parallels Tools. Then click on the Virtual Machine option in the top Mac menubar and select Install Parallels Tools.
Make sure all of the latest Windows updates are installed. Go to Start > Control Panel > System & Security and click on Check for Updates:
Impossibility to play video
Download and install K-Lite Codec Pack.
Make sure the player you use has the latest updates installed. Click on Help > Check for Updates.
- Try to use some different player to run video, for example VLC Player.
Windows applications video performance
Click on Virtual Machine option in the top Mac menubar, select Cofigure > Hardware and make sure your application system requirements are met. Tune the settings if needed.
Quit Coherence view mode if you were running your virtual machine in it. Switch to Window mode.
Tune the settings of your application to lower graphic and performance configuration.
In the configuration window go to Options and make sure that Power option is set to Better Performance:
In Configure > Hardware > Video set the amount of video memory according to the Windows application requirements. Set the amount of video memory to 256 in case you do not use any particular graphical applications.
- Turn off Aero theme on Windows side.
Submitting a problem report
If the issue is still not solved or you have difficulties with any of the steps outlined above, please submit a problem report from Help menu > Report a Problem.
Remember the Problem Report ID and keep it for technical support department. Contact Parallels Support.
Note: to speed up the issue resolution process, you can send the results of the above troubleshooting and a Problem Report ID while submitting your support request.