Mysterious missing server address

[Doc Pixel]

Hi, I'm a PC user cautiously peeking in the door. I've got a Mac problem, and hope someone can help me.

My dad is a Mac addict, and had a stroke. He got off really lightly, but he's struggling to get back to using his laptop.

Anyway, he suddenly can't connect to the net. When we try, the server address is blank. Can someone tell me where to look for it? His ISP is Seanet.

Please keep in mind, I know nothing about Mac OS, so detailed instructions would be good...
Thanks,
Doc