Every printer problem that I have had since 1996 (other than a mechanical hardware problem)...ultimately was resolved by uninstalling and then reinstalling the noted printer.
As for why these problems occur...any number of reasons, with my chief token answer being file corruption, either in the printer software or the drivers.
Because printers tend to spew a flurry of files and registry entries everywhere...I suggest doing a manual search of both the files and the registry to eliminate any entries that relate to the manufacturer of your printer...before attempting a reinstall.
If journeying into the registry, I further suggest that you take the normal precautions suggested by many when about to make registry changes.http://mikescomputerinfo.com/xpregistry.htm
Backing Up and Restoring the Windows XP Registry - http://www.theeldergeek.com/windows_xp_registry.htm