As weird as it seems to anyone who used it before, most of the time explorer view does not work until some steps to be followed, but in my case it was working and sometimes randomly not working !
After spending hours of troubleshooting and collecting logs, Network traces, Fiddler traces, etc. I reached the solution from the Network trace.
Although it seems strange, it was sending a PROPFIND request to the root directory "/" which was actually deleted. So, I came up to this important article that states that you must have a root site collection in your SharePoint web application in order to keep it in a supported state.
And actually that explained it and solved the strange behavior as well.