Nevermind, i found a solution on another forum. Here it is if anyone else has this issue.

1) First open your "my documents" folder and check if a gtr2 folder has been created there, if it is the case then delete it!
(since windows vista, gtr2 will create a setting folder there if you forgot to set winXP / Admin rights on EXE)

2) Now you absolutely need to right click on all EXE (gtr2.exe, gtr2config.exe, etc ...) in order to enable 2 things:
- windows XP sp2 compatibility mode (you can also try win7)
- check administrator rights

3) Then reset gtr2config.exe with any 32bits resolution and not 16bits as alex said (1980 * 1024 * 32), choose dx9 shaders and DO NOT check AA / AF (do that in your nvidia / amd setup).

4) run gtr2.exe and check ...

5) if lcd still doesn't show up then check key assignment in menu: Motec can be disabled / enabled (lcd off / on), but by default the key is not mapped if I recall ... try to hit "M" key in case