@leondicta
Hi,
im not french, i try it in english:
First of all, your folder structure looks awful 
delete the .7z
on your folder.
The easiest way ist to convert to .chd. Result is one file per game.
Search the www for Dreamcast gdi2chd converter
.
But you can edit your existing files also manually (more work).
Example with Crazy Taxi:
Foldername is Crazy Taxi
Copy the gamefiles (*.gdi, *.bin and maybe *.raw) into the Crazy Taxi Folder.
Reboot and test if it works.
When not working:
Open your Crazy Taxi Folder.
Rename your Crazy Taxi *.bin filenames (i only see .bin files on your screenshot).
before
Crazy Taxi (Track 1).bin
after
track01.bin
Do the same with Track 2 and 3
Now open the Crazy Taxy.gdi with an Text Editor like for example Notepad++
To understand:
The *.gdi file is only a cuesheet (the same as a *.cue on PSX System).
After opening the .gdi file you see maybe this:
3
1 0 4 2352 "Crazy Taxi (Track 1).bin" 0
2 450 0 2352 "Crazy Taxi (Track 2).bin" 0
3 45000 4 2352 "Crazy Taxi (Track 3).bin" 0
rename the filenames
inside the gdi:
3
1 0 4 2352 "track01.bin" 0
2 450 0 2352 "track02.bin" 0
3 45000 4 2352 "track03.bin" 0
Save and close the .gdi file.
Reboot and try again.