When I go to open lightroom a message pops up and says "lightroom encountered an error when reading from it's preview cache and needs to quit" I have already restarted my computer, that didn't do anything. I then uninstalled and then reinstalled and still getting the same response.
Open the folder containing your Lightroom catalog. Locate a folder with the extension .lrdata and delete that folder. Do not delete anything else. Then restart Lightroom. It will start building a new previews folder.