Check three things. First the batteries. Press your battery check button. If the power indicator light does not come on then replace them. If it does then try moving your shutter speed dial from one extreme to the other. Sometimes the shutter can stick on a speed and doing this in a few cases might free things up. If this does not work then open the film back. If there is film in it, mark the exposure number and rewind the film until you feel it come loose. Do not rewind into the cannister if you want to expose more frames on this roll. To do so, just make exposures with the lens cap on and continue until you get to where you left off. Back to why we're opening the camera back. Look at the shutter curtain. The end should not be visible. If it is then see if it is perpendicular to its line of travel. If it is cocked slightly off then it could be jammed. Take something and press on the edge of the shutter curtain and see if it snaps back over on the tension of the springs. If it does then do so for the inner curatin.
I suggest the last because if it is none of these and it is more than likely a blown electronic capacitor that, unless you are mechanically inclined and choose to do yourself, you could replace it on ebay cheaper than having one repaired.
(Edit: Also, knowing whether the mirror is locked up or not would be useful to know.)