I'm with the first response but with this added: AFTER opening the cover if it has one and trying switch, if it doesn't work, check the fuse. My first fan experience was when after playing with all the setting and such I thought I had fried it. Nope, just forgot that the fan cover had to be open for the switch to work. Hmm, now that I mention it, its another thing to check - the cover disable switch could also be stuck.
If hunting for a new fan, they don't come cheap. I'm guessing on the size etc but here's one and since its Amazon you can probably return it if it doesn't work out:
Fan-Tastic Vent 4000R Off White Vent with Reverse Switch