Please do the following steps:
1. Is there anything added to your Guild Wars folder? (Default area: C:\Program Files\Guild Wars) Is there only the templates folder, screen, Gw.dat, Gw.exe, Gw.tmp, and Gw.dmp? If there is any other files get rid of them.
2. Try disabling your firewall and anti-virus program and run GW again.
3. Try updating all your drivers for your PC.
4. If all that doesn't work, try reinstalling GW and re-downloading the DAT file. Put /image after Gw.exe target to DL all of GW.
Please try all that and report back.