Hey, thanks to everybody who posted and suggested help. I've been running calibre on Windows 8 for over a month with no problem, but the problem was with my account as JSWolf suggested. I had done everything AnotherCat had said, to no avail but turns out the solution was far simpler. I just had to edit the calibre shortcut in the Start Menu Program directory, and set it to "run as administrator".
Thanks everybody for the support!
P.S. Feel so foolish now >.<