La synchronisation a échoué

[abdo]

I think this error message is a certain indicator that you’re using Anki 2.0.
See this post for a way to locate the older installation:

Sync and version issue

maybe you have installed 2.0 and 2.1 at the same time and in the startmenu you see a link to the version for 2.0? For certain upgrades uninstalling the old version first was recommended, see https://apps.ankiweb.net/ Recent Anki versions should be in C:\Program Files\Anki whereas old versions were in “C:\Program Files (x86)\Anki`. Check if you find the latter folder in your windows explorer. Then I’d try to delete this and the start menu entry: From the control panel I’d try to uninstall all …

Try a recent version after deleting the older one.