Bon j'ai trouvé, j'ai effacé toutes les partitions du disque :
J'ai tapé shift F10 à la sélection des langues dans l'install de windows 7 pour faire apparaitre la ligne de commande et j'ai tapé :
(http://www.sevenforums.com/tutorials/26203-convert-gpt-disk-mbr-disk.html)
3. In the command prompt, type diskpart and press enter.
4. Type list disk and press enter.
NOTE: Make note of the disk number (ex: Disk 1) that you want to convert to a MBR disk.
5. Type select disk # and press enter.
NOTE: Substitute # with the actual disk number that you want to convert to a MBR disk. For example, select disk 1.
6. Do step 7 or 8 below for what you would like to do.
7. To Use the "Clean" Command to make Disk Unallocated
NOTE: This is the easiest method. It will wipe the disk clean all at once leaving it as unallocated space afterwards.
A) In the command prompt, type clean and press enter.
B) Go to step 9 below.
8. To Manually make Disk Unallocated
NOTE: This method has you manually delete each volume on the disk before converting the disk to MBR.
A) Type detail disk and press enter. If the disk does not have any volumes listed, then you can go to step 8E below.
NOTE: This will give you a list of all the volume numbers on the selected disk number that you will need to delete in steps 8B and 8C below.
B) Type select volume # and press enter.
NOTE: Substitute # with a volume number listed in step 8A. For example, select volume 3.
C) Type delete volume and press enter.
D) Repeat steps 8B and 8C for each volume # listed in step 8A until you have deleted all volume #'s.
E) When finished, type select disk # and press enter.
NOTE: You would use the same one from step 5 above. For example, select disk 1.
F) Go to step 9 below.
9. Type convert mbr and press enter.
10. Close the command prompt.
11. You can now create partitions on the now MBR disk if you like.
NOTE: Restart the computer if you did step 2 instead.
