Networking pop-up box on start up

When I start up Windows 98, and before the desktop fills up with its icons, I get the following box popping up :-

“Enter Network Password
Enter your network password for Microsoft Networking
User Name
Password”

. . . and two check boxes for “OK” and “Cancel”. The “OK” box has to be checked before I can proceed into Windows.

How can I get rid of this ? To my knowledge Networking has never been installed on this PC, except when I installed and then deleted it in the vain hope that this box would disappear !