I know this might not be worth it to you, so what I suggest, IS.
Move your Gw.dat file (you should know which 1 it is, as it's quite big, mine's around 1.5GB) in your C:\Program Files\Guild Wars directory to your Desktop or someplace, un-install Guild Wars but make sure your Gw.dat file is still there on your Desktop, then download the Guild Wars client of the Website, here:
http://www.guildwars.com/downloads/gwsetup.zip
Then run it, if it works, good, just move your Gw.dat file back to your Program Files of Guild Wars again.
Note: I tell you to move your Gw.dat file is that what holds all the info so you don't have to load all the Locations and Maps again.
+ Are you having any other problems with your ISP lately?
[EDIT]
Although, you may have to keep your Gw.dat file deleted and let everything re-download as it may corrupt something to do with the BETA PvE Factions event coming up.
TRY THIS FIRST BEFORE ANY OF THE ABOVE:
Move your Gw.dat file, start Guild Wars up so it makes a new Gw.dat file in your Program Files and see if it works.