The DWM.exe is an important part of the system, hard to believe it is not running, but you can check that in msinfo32.exe and look at the Loaded Modules and Running Tasks. It is not listed in the Services Panel. If it isn't running, you might try to start it by double clicking the actual exe file in Windows\System32 folder.
There is another service that provides the DWM.exe startup and maintenance services named Desktop Window Manager Session Manager (UxSms) in the services panel. You might check it and make sure it is running and set to automatic start. In the registry, the starting entry should be in HKLM\system\CurrentControlSet\Services
You might check the Event Viewer to see if any...