Knowing which camcorder model might help.
You "changed the lens". I don't know how you did that unless you are using one of the NEX VG models... but that would not be HDV.
One of the miniDV tape based HDR-HC, HDR FX or HVR-Z series seem more appropriate. The model number is on a sticker on the bottom of the camcorder. In any case, the generic response to start with is for you to read through the manual and find the instructions on resetting the camcorder to factory default. Sometimes there is a reset button. Sometimes there is a menu selection. Sometimes it means removing the battery and a little button battery (that maintains settings, date/time, etc.).