in's Creed 2 achievement help. Glitched?

OK. I'm playing AC2 around the fourth sequence. There is a problem. Every time I earn an achievement, the banner pops up, however, I go to view it and my profile says I have 0Gamerscore. The game saves and I dashboard to see my achievements. It has my usual amount there, however, the achievement I just got doesn't appear. When I start my game again, the story continues from after the point where I got the achievement. This problem occurs for ANY achievement I earn, not just main story line achievements. I'm thinking about modding my gamerscore just for those achievements that I earned and didn't recieve. Does anyone have any advice to resolve this problem. 5 points to whomever solves it first. Thanks in advance.