I just got this Vivitar 383 flash from eBay. I tested it out when it got here and it was working great, then my brother got eager and started using the flash by firing the test shots. Now, the flash won't fire, the sensor and everything else works but the flash won't fire. I changed the battery and same thing. I tried using it as slave and on the hot shoe and still won't fire. Any help? I need to use it by the 13th so I'm a little worried.