Problem with credential for internet connection

[Lookone77]

Hi,
I’m new in the forum.
I hope you can help me to solve a problem with my Windows Vista Home and the internet connection.
When I’m in my university I have to use the MD5-Challenge as authentication to access to the LAN internet connection.
Now, after some problems with the nCleaner software (a registry maintenance software), the “pop up” windows where you have to click on to activate the main window where you have to type the username and password, doesn’t appear when the LAN cable is plugged on.

I’ve already tried to install again the registry key (provided by the informatics service of my university) to activate the MD5-Challenge option in Vista but it does not solve the problem.

Someone have already experienced something like that?
Someone could give me some advice to try to solve the problem?

Thank you.
Regards,
Luca

P.S. sorry for my English, I hope you can understand me.