You're probably going to have to re-install, assuming that you still have the discs for Vanilla, BC, and Wrath still. That, or just install the patch and everything and see what happens afterwards. Though, be forewarned there are two more patches after 4.0.1; patches 4.0.3 and 4.0.3a.
The 14gig patch was for patch 4.0.1, which included all of the class changes and stuff, and also had the new launcher with it, so it's a legit patch and everything.
The other option is just wait until Cataclysm comes out and buy a hard copy of the game and just install from the disc.
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