From the info: A PS4/PS3 slide switch on the base ensures optimal compatibility with both systems.
Do you have it in the right position? Have you read through the instructions? Are the games compatible with the T300 RS? Are you using the steering wheel for PS3 or PS4? Latest firmware installed?
Otherwise contact Thrustmaster support directly:
http://ts.thrustmaster.com/ger
(To get access to the extended support menu (mail address and phone number) you have to log in).
Here is the latest firmware:
http://ts.thrustmaster.com/ger...
Manual (German from page 38 in the PDF):
http://ts.thrustmaster.com/download...
And further help topics:
http://ts.thrustmaster.com/ger...