Okay you may have reconnected improperly, are you sure you have the control cable from the changer to the main radio unit connected?
If that checks out, then you most likely damaged one of the internal components, not necessarily when you took it apart, but when the 2nd disc was inside. When jammed like that it is easy to cause damage to the laser and transport assemblies.
You can attempt to clean it by blowing out the disc tray/slot area with a can of compressed air for dusting computers (keep the can upright only so you don't get chemical propellant on the lens).
Next, reset the system by unplugging power for an hour
press and hold the power button for 60 seconds, keep holding while plugging back in, and for another 60 seconds after.
If none of these help, then there is an internal hardware defect, which will need to be repaired.
If it gets to that point, I can advise you on service options.
Let me know the results, and I'll advise further, if needed.