X Axis move in only one direction after Firmware update

Hi, I have a big Problem.
After expanding the print bed to 40x20 cm with the Velleman kit, and changed the Belts to GT2, I downloaded the new Marlin Software (using Firefox, as there were posts that IE may damage the download) and changed the values, to correct ones (80 steps/mm, Speed 200mm/s max, X-Limit 400 mm, Y Limit 200, Z Limit 210 (was 220)). Also changed the Values for Z and Extruder for using the Z-Rod and 0.35 mm hotend usable.
Arduino Studio Version is [color=#FF8000]1.0.6[/color]. As I heard, newer version may render one axis working only in one diorection. Also 1.ß.4 and 1.0.0 tested with same results.
After Update, the X motor did not move backward, only forward (Y and Z Steppers are working as expected). Attaching a new Motor to X did not change anything. Swapping Drivers did not change anything. Using different Mainboard after update did not change anything.
Is there anything else, I can try, to fix this Problem? Please help!

This sounds like an open on the X end stop.
Check the wiring.

Thanks. that was in fact the reason!

Glad you hear it’s working.