Hi Sandy,
I'm not a Windows user so can't help with specifics... sorry :)
Please do fill out a ticket to our Support team:
http://www.macprovideo.com/support/
They'll get back to you as soon as possible and help you resolve the issue. Please do let them know what version of Windows you are running and any other details that might be useful.
In the meantime I might suggest restarting / rebooting your PC - log out and then log back in to NED (using the exact same username and password you used when purchasing your tutorials) and see if the issue persists.
Best
Rounik