Quick guess, its malfunctioned. Those are notorious for failing, and its probably time for a new one. Can you get access to a light dimmer? That might hold you over until you can get a better/functioning thermostat such as a Ranco from www.reptilebasics.com.
Well that's just flat out annoying.
Unfortunately, no, I can't. I still have my heat lamp though, so I can hook that back up until I can get enough money to afford something like the Ranco that you suggested.