roll back driver
you got one of few issues.
1. Your not the installed admin user on your computer. (each manufacture puts a Hidden Admin account on each computer) its a Dell or Hp etc thing not a Microsoft issue.
To become hidden admin
(do this step last if no others work)
2. You need to roll back your drivers and install the ones from the Phone NOT the ones from Windows. So to roll back to starting position or delete them go to this Guide here
Next you need to Keep windows from grabbing the Samsung drivers from Windows which can be the issue
Go here for help if you don't know how to do this
3. You need to uninstall and the drivers for the phone, and download the new drivers from Samsung and/or delete the drivers and ALLOW the phone to install them only
To do this go HERE
This above link is to delete the old USB drivers. IT WILL DELETE MOST OF THEM, dont worry the devices will auto load when you put them back into the computer.
IF 2 or 3 DONT work then do step one. Between each step do a rest, and keep all devices of USB unplugged.