MANY THANKS for the following tip: there was realy a version of Zone Alarm firewall installed on the PC.

After a restart, the Internet connection (Port 80) was open for about 8 or 10 minutes. Then, the Port was blocked. All other Ports were open.

The only solution was your description:

3 [...] Navigate to HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\vsdatant
4 Click start in the right pane and modify the value from 2 (may be other than 2) to 3. [...]

Many Thanks!

MB

Solution posted online