This is about the worse thing that can happen to your ac. When the compressor locks up like that it is due to internal, catastrophic failure.

Don't even DREAM about simply replacing the compressor and being done with it. That will result in almost immediate failure of the new compressor. Remove the compressor and FLUSH EVERYTHING in the a/c system. FLUSH, FLUSH and FLUSH again. When the compressor fails like that bits of debris are strewn THROUGHOUT the entire system.

After THOROUGH flushing, replace the receiver/dryer, add 6 oz. of mineral oil, evacuate and charge with R12. If the system has been previously converted to another refrigerant this would be the perfect time to take advantage of the fact that R12 prices are falling like a rock.

Good luck,