Can you post your Revit journal?
Also check if you see Dynamo or anything with a similar name in the details tab of task manager.
Try right click and Maximize:
If @Kulkul’s suggestion doesn’t work, make sure your windows has the focus of the Dynamo window by selecting it, then try holding Windows key and pressing left or right. This problem is common when switching between 1/2 screens in my experience and maximize often wont bring it back.