I was playing some Skyrim earlier when my cat rubbed up against the console and turned off my 360. I left it off and went to run some errands. I returned to continue playing later on and it took me a while to realize my two thousand achievement points were gone. All of them. I checked to make sure I was signed onto MY Xbox Live account and I was. I logged out, logged back in and they were still gone. I restarted my 360 and the same thing. Just before posting this I visited Xbox's site on my account and my account looks like it's been reformatted. Is there anything that can be done about this?
If you are experiencing issues with zero Achievements and Gamerscores you may need to delete and recover your profile. Details on how to do this can be found here.
Your cat is off the hook then...
Microsoft is now saying that they have resolved the issue.
The xbox support twitter account tweeted that you should try signing out and signing back in again, and it should fix the issue. Judging from replies they give to various users, they are looking into resolving specific issues, so if this doesn't solve it, you could try tweeting to them, if you have a twitter account.
Also, a post by Mister Fizer on the official xbox forums states the following:
Please note that this will remove any achievements you might have earned since the issue began, however, they can be re-earned.
Further to that, Kotaku says that
Microsoft reached out to us this afternoon, saying that "all achievements earned during the outage will be resolved within 24 hours."