Laptop network works intermittently

[MR ZenWiz]

I have an HP NW9440 laptop running Xubuntu 12.04 that is having an
interesting issue with its wireless connections.

Example: I'm on vacation in Michigan at my sister's house, and last
night I powered on the laptop and it found the house wireless network
without any trouble and connected through it.

This morning, the same password for the network is not working and the
laptop can't seem to make the connection.

This has happened at a friend's house back home where they have a more
secure hidden network and the password hasn't changed, but for some
reason the laptop can't seem to make the connection any more.  One
time they rebooted their router and all was well, but the last two
times that was no help.

The second-most annoying part is that the network retries every few
minutes and pops up a new window for the password (which hasn't
changed).

What am I looking for to make this stop?

Thanks!

MR