Help please,.temperature sensor outputs show 999.9....

Dear colleagues,
I am very new to industrial and now I am trying to fix the plastic injection machine. On terminal display, 5 sensors outputs show 999.9 and machine can not start. I changed the sensors, but the result is the same. Only changing to 888.8. wiring from sensors to control board is checked and ok. Any idea ? please.
regards,

PLC brand and input module part # would be helpful, but if I had to take a stab at it, you could have lost DC power to your input board and so everything is defaulting to possibly a failsafe high temp condition. Or they are reading negative and the scaling on your display clamps to max value expecting an unsigned integer, again due to loss of DC power. A signed integer value -1 for example, reads 65535 as unsigned.

Thank you robertmee, for your advice.
I'll check the psu and mail back again what's happening.
See you.

Dear robertmee,
Yes, there is a negative voltage regulator ic( 7905 )and it was not working properly. So, I change it and now the display shows 760.00. The positive voltage regulator is ok. output 4.99V.
The controller is A62B. There are 3 i.o ports. I can not get it manual.