I had this problem a few years ago. Had to dump the memory by holding 2 keys and powering on(beware, you will lose ALL parameters including the parameters for number of axis, numbers of tools, etc.). You have to enter so many parameters in octal(10 or 20 parameters) before you even get the familiar screens. Once you get that working you can setup communication and upload them from a PC. At the time I didn't have the parameters on PC..... oh that was fun..... All by hand, then try and figure out which ones were changed through the years... needless to say it was buggy for a little while until the parameters were straightened out. BACKUP PARAMETERS before something like this happens to you!
This problem can be caused by power spikes, loose connections on boards, poor power supply, backfeeding circuits with high voltage, etc etc etc...
Jack of all, master of none
Galveston, TX