Diagnose Siemens-Omron Axis Issue

My tmachine runs on a Siemens PLC and Omron servo drives. During the homing routine the X-axis servo no longer responds, even though the other axes behave normally. It used to move without any problem and I have not touched either the hardware or the software since the last successful run... (Budget: €250 - €750 EUR, Jobs: Automation, Control Engineering, Debugging, Electrical Engineering, Electronics, Engineering, Microcontroller, PLC, Technical Support, Troubleshooting)