Desktop and laptop networked and working fine until today.

Using XP on both machines and a Linksys BEFW11S4 router...

The laptop communicates with the desktop normally. Internet, file transfers
etc all function as they should.

For reasons unknown, when trying to access the laptop from the desktop, I am
now prompted for a password to connect to the laptop?

Would anybody know how to I can eliminate this password prompt and
reestablish a network connection to the laptop?