@poppingmythik Unchecking the box in Steam did uninstall the pack, but it didn't remove the associated registry entries, or at least it didn't last time I tested. If you do want to uninstall University Life, you can uncheck that box again, then delete the two relevant registry entries.
Hit Windows key-R, enter "regedit" without quotes, and then click File > Export and export a copy of your entire registry, just in case. (Deleting the wrong entry can brick your entire computer, so it's best to take precautions; you can reimport your registry as-is by double-clicking the saved file.) Next, expand this path:
HKEY_LOCAL_MACHINE > Software > WOW6432Node > Electronic Arts > Sims(Steam) > The Sims 3
HKEY_LOCAL_MACHINE > Software > WOW6432Node > Sims(Steam) > The Sims 3
In each section, you'll find a folder for the base game and each pack you've installed. Right-click on the entries for UL and select Delete, and the game should load without the pack installed.
By the way, you can also export a single section of the registry if you want, for example preserving the two Sims 3 sections and restoring them alone as needed. It's fine to restore the entire registry right after you've changed something, but you wouldn't want to use a weeks-old copy: you might have installed something in the interim that would then have its own registry entries wiped out by the restore.