I need HELP....!!!

Hi, My name is Carl and I run a Heian NC-431P CNC machine for this small company in Sebastopol, CA. where me make world class Wood Furniture. anyways, just recently my M92 command (All heads off) stopped working. so at the end of my tap/cnc/nc file I'm running, my head won't shut off nor will it go back to it's starting point. So now I've had to delete all the M92 commands and replace it with the appropriate M command for the head I'm using at the time, to make it lift. for example: M12 for head #1 up, M22 for head #2 and so on..! except when I use the M42 command to lift head #4, it won't go up. so I have to go to the console and manually lift the head.
So I'm not sure what my problem is..? Is this a hardware or software problem? have rat's been chewing on some wires someplace...?