You may have bumped something and broke a seal, and it leaked all the r12 out. Take it to a shop, and have them evacuate all the R12 out of the system. They should do it for free, since R12 is so expensive, and it's free r12 for them. Then buy an R134a conversion kit, and charge it. Get a bottle of UV leak detector also, and check for leaks. Make sure you don't charge it over 40psi, but no lower than 30psi.