Better follow Dave Sample's advice, sounds like you just got something assembled wrong. Here's a few more ideas:
1. First, disassemble the pistol again (be sure you have some good instructions on disassembly and assembly - let me know if you need more instructions as this can be tricky, but is not really difficult if you know the tricks).
2. The "cylinder hand" spring may have been crimped in the re-assembly or you may have dropped the spring and plunger into the wrong hole in the back of the frame. Check this out.
3. I have found that it is very easy to incorrectly position the "cylinder stop" plunger and spring during the re-assembly of the grip frame. Be sure that after the grip frame is in place the cylinder stop works correctly - it should be sticking up out of the frame with significant spring pressure, but should be easily pushed down with your finger, and should then immediately pop up again. You may have to take it apart, reposition the little parts and then try again 'til you get it right.
Those are the two main assemblies that control the cylinder rotation and cylinder locking and unlocking.
4. I am assuming that you just polished the hammer sides and the area where the sear nose scrapes along the hammer before engaging the hammer full cock notch and that you did not touch the hammer full cock notch? In that case this should not have caused any problems.
5. If you removed the cylinder stop trip plunger and spring from the hammer, better take it out again and double check that it is correctly installed in the hammer. That could affect the locking and unlocking of the cylinder if it is not operating freely.
Good luck,
-scruffy