Updated:
I’ve solved this issue.Incase anybody search for this topic,I tell what I do.
1 Open C:\Users\ YourUserName\AppData\Roaming\Dynamo\Dynamo Revit\2.19 folder
2 Remove all folders to other places
3 Open Revit again and dynamo opens
4 Copy back package folder back
This is strange issue,I never met this before.But this way which may seem not smart but it’s effective.
The post could be closed now.