The bad lag story

So, I just came back to the game roughly 4 days ago. Keep in mind that I have a medium computer, running a AMD 64bit 3000+, X800xl and 1GB of RAM.

1) I install the game via the download version on the GW website.
2) I begin to play and I have a consistent and laggy 20 FPS main menu and then when I get in the game it ran at about 15-22 FPS. Also, the terrain has a bunch of outlines of squares. ( http://tinyurl.com/2kfua5 )
3) I am recommended to installing new VIA and AGP drivers. I do so and the low FPS is fixed. I am now running at 68-93 FPS in the same areas.
4) I go to bed, and wake up the next morning and it's back to low FPS. I decide to reinstall the game with the CD's and it didn't fix the problem.
5) I post back on the forums and am recommended to reinstall directx 9.0c and install the catalyst 7.4 drivers.
6) I install them and restart my computer. My game then ran at 68-93 FPS again. Not only that, but the squares are gone! ( http://tinyurl.com/2whfhv )
7) I leave for a few hours and come back to play again. My FPS was down to 15-22 FPS again.
8) I decided to defrag my computer. It fixed the FPS again and it was back to a stable 68-93 FPS.
9) Just about 3 hours ago, my game went back to 15-22 FPS. I was fed up with it so I copied my .dat file to My Documents and proceeded to uninstall the game and install it via the download version. When I finished the install and downloaded the client data, I got in game and the terrain was back to having squares! Not only that, my FPS was back down to 15-21.
10) I decided to delete the .dat file and copy paste the old one into the folder. I then went into the game and everything was fine. It has remained fine since.

Figure that one out...

Update:

I turned on my computer this morning and I had a bit of bad FPS in the game Mafia. I tried out Guild Wars and it was back to the 15-21 on the main menu which means it was in low fps mode. I restarted my computer and it was fixed, even though I had JUST turned it on previously. It seems that sometimes it boots in normal fps and sometimes it boots in low fps. ....