What happened to my achievements?

The thing is Bong, with my 360 I can put a game disc in and start to play the game without signing in to any profile on the console.

Yes. I played offline for about 2 years. But the worse part is that in both Fallout games, the achievements disappeared from my console as well. From Fallout:New Vegas, I only lost a few, I can deal with that. But most of the achievements from Fallout 3
have disappeared. I was just wondering if anyone else has had this happen and may know the cause. Also, I have unlocked some of the achievements in Gears of War but the game doesn't even show in my list, let alone anything I unlocked. Thanks for any insight
you may have.

I am using the same account. But before I joined Xbox live, I had a whole bunch of achievements in Fallout 3 and Fallout New Vegas. In Fallout 3, one that disappeared was one I remember most vividly. "Those!" was hysterical because I used a grenade to blow
up a giant ant, it flew up in the air, landed on a shed roof and slowly slid off, almost like it was using real physics when sliding. "Those!" is one that disappeared. I beat both games and even restarted both going in a different direction but now Fallout
3 says I only have like 3 achievements but I had most of them. Idk... Just a little annoying that they all disappeared.

I've decided not to pursue this further as a rep from Gamestop answered my question. Xbox support referred me to the forums and I guess I'm not as savvy as those hooked on Rock Band and Kinect Sesame Street TV. I thank you, Paraffin Alien for your attempts
to help.

Now, let me see if I fully understand what is going on here.

It now seems obvious to me that when you started using your console you basically continued to game like you would on the original Xbox, without having to create a profile.

So now, you have just recently created an XBL profile on your console and you have found that non of the achievements you have unlocked show up on your recently created profile?