Certain programs/processes may effect the activation of your game client. In this case, you can resolve the problem by closing all processes
 Press Windows Key + R to open Run dialog box
 Type in 'msconfig' and press Enter
 Select 'Selective startup', and uncheck 'Load startup items'
 Select [Services] tab (above)
 Check 'Hide all Microsoft services'
 Click 'Disable all'
 Click Apply button and then click OK.
 Click Restart (Reboot PC)