Laptop no longer able to get online, except at home

My XP laptop suddenly stopped being able to connect to the internet at a
friend's house, either wirelessly or plugged directly into the cable modem.
Before that it connected wirelessy just fine for several days.

Nor can it find the other nearby wireless networks (neighbors, etc), which
it also could do until yesterday.

BUT - it still connects just fine at my own house, both wireless or plugged
in directly. And, as usual, it detects my neighbors' networks.

At the friend's house, I tried restarting the computer, unplugging and
restarting the router, including waiting 24 hours.

No changes of any kind were made to the computer (connection settings,
installing hardware, clicking on suspicious websites or emails etc.)

This is especially perplexing for many reasons:

1) How could I get online just fine at the friend's house, then suddenly not
be able to?

2) If it was a glitch between my computer and her ISP, then why doesn't my
computer show any available wireless networks at all?

3) How can such a problem only happen at her house but not mine?

Thanks much.. this one has me stumped