I've been play BG, (the original, not EE) for a couple of hours but after returning to Nashkel from the Gnoll Stronghold whenever I enter a building the game, which is running in like 800x600, freezes and the game goes into windowed mode. I have unistalled it multiple times and the only mod that I have installed is the BG1FIXPACK. I am unsure of what else I can do and I hope that my saves aren't corrupted....Do you guys haVE ANY IDEAS?

You say the only mod you have is the BG1Fixpack, but if your playing @ 800x600, you must have installed the widescreen mod.
Did you change the resolution after you started the game?

No, I dont have the wodescreen mod, it is running at its native res, though i did briefly install the widescreen mods, but afterwords the game began to lag so I uninstalled it.

The native resolution is 480x640, if you saved the game @ 800x600 with the widescreen mod installed & then removed it, you will have to start a new game.

Also, if you are/have been using the wide screen mod, there have been problems with older versions when entering very small areas such as buildings. Many of these have been fixed in version 3.06. It could be useful to remove the wide-screen mod and then re-install the newer version if you still wish to use it.