Wireless problems.
Okay, so I have a WRT54GL running DD-WRT. Many people have those. The problem, however, started when I moved my desktop PC from wireful to wireless. For some reason, My laptop (also wireless) could not reliably access windows file shares. It would access some of the folders some of the time, and most of the folders none of the time.
I toiled and troubled over it to find out what was wrong, but no