Hi Waldfee,
See #2 on the help list below but also read the rest as you may need the advice someday.
G25 Force Feed Back (FF

cure and other wheel tips.
1… PROBLEM: Sometimes when you try to drive there is no response from the wheel or pedals at all.
REMEDY: On the race menu screen go to ’OPTIONS’ > > ‘CONTROLS’ > > ‘CONTROLLER FORCE’ (3rd steering wheel fig on bottom right) > > ‘FEEDBACK EFFECTS’. Now press on the left or right arrow to change the force and then change it back to its previous setting. You may feel the wheel jolt that is OK. Now try driving, it should be alright now.
2... Sometimes removing the USB plug and re-inserting it clears a fault. I have heard that a 'USB HUB' can cause this type of problem so if you have your wheel plugged into one try plugging directly into your computer instead.
3… A good tip when setting your wheel and pedals up is to ALWAYS set the brake before the throttle. The reason for this is simple, there is a glitch and if you set the throttle up first you will find it is not very responsive to the touch.
I run my game by loading it from the 'Logitech Profiler' which installs itself on the bottom right tool-bar of the computer desktop. You can set the controller up on here for all car games needed but sometimes like GTL it gets corrupted and needs re-installing.
Try un-installing and reinstalling both GTL and the Logitech profiler. Your car & track files will not be overwritten doing this but save your 'UserData' file on GTL just in case.
Hope it works for you.
Gee-Deeman