Can no longer copy files from one pc to another

Hello

I had my PC and Desktop networked together for a couple months. All
was working fine. Tonight I tried to copy some files from one pc to
the other, and thought I couldn't remember my login/password.
After trying a bazillion times....I realized that it wasn't that I I
was having a mental laps and forgot my login....there was something
else going on. The Desktop is no longer prompting me for a network
login at bootup. Don't I need to log into the network on the PC for me
to be able to see that PC from my laptop? Here is my set up.

Desktop running Win2000Pro hardwired to router.
Laptop running XP-Home Edition, connected wiresless to the network.

I can ping each PC from the other.
Workgroup names match on both, and I've never changed that since it was
all working.

Is there a way to reset the network passwords on these machines? Last
thing I want to do is reinstall windows. I tried a restore on my
laptop to a week ago, but same thing.

Thanks for any help you can give me.

Thanks, pam

I should also probably mention that both PC and Laptop have no problem
reaching the internet.

Thanks again.
Pam