Parait qui ya une manip a faire c´est ecrit sur le site de bungie:
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Note : A rare bug has been discovered that sometimes results in improper text display in the game UI. Basically, you won´t see any text at all. If you encounter this issue, you can fix it yourself by doing the following:
1. Restart your Xbox 360
2. Boot up the Halo 3 Beta
3. While the Halo 3 Beta is loading, immediately press up on the D-Pad and hold the A button until you see the Bungie logo. If you perform this correctly a dialog box will appear confirming maintenance has been done to your system.
4. Resume the Halo 3 Beta!
"