It seems to be that some windows process is blocking it.
Please disable all start up items , restart the machine and then try.
Check here on how to disable start up items : http://www.howtogeek.com/74523/how-to-disable-startup-programs-in-windows/
Thanks for your suggestion ! I tried doing that but it makes no difference
In another post I found the answer from Staff member Tanuj- that fixed this problem for me.
- Please open Lightroom , and then open the Task Manager.
- Set the Priority of Lightroom.exe to High, close Task Manager.
- Please reset the Preferences of Lightroom by holding the Shift and Alt Key and then open Lightroom.
- Restart the computer, and then see if it helps.
My Screen-clips :
In Task Manager Right-Click on the App Adobe Photoshop Lightroom-
Select the option "Go to details"-
Right-Click on "Lightroom.exe" to Set Priority to "High"
Thank you for your help !! Problem solved