I answered some question in the MSE and I earned some up votes, but I got no change in my total reputation and I don't know what's the problem. I have this problem for three days and just I earned reputation for accepted answers, not for up votes...
The daily gain of reputation from up-votes and getting proposed edits accepted is limited to 200. After that point up-votes have no more effect on the reputation. The counter is reset at the beginning of each day (UTC).
Accepted answers and bounties are not affected by the cap, which is why it is possible to get more than 200 points a day.
Another possibility (not relevant in the current case) why one does not get reputation from up-votes is that the post is in Community Wiki mode.
Moreover, it should be noted that the counter in the top-bar only shows an increase in reputation over the last increase. This entails that if, for example, one loses 20 points for some reason and then gets an upvote the counter will not indicate this as one is still below the last reported increase (in this scenario, the upvote had still an effect though).