Based on what you are describing it sounds like the iPod believes the Hold switch is in the locked (orange showing) position. Try toggling it between the two positions a few times to see if that changes it. If it doesn’t open the iPod back up and try re-seating the cable running to that switch. If re-seating it does not help, then the hold switch was likely damaged during the repair and will need to be replaced, happened to me on my 5th gen as the battery tried to carry the cable with it, tearing it.