problems with font

hello,

My language is latvian and we have characters like ā, ē, ī and so on, but it shows ? for those ones and I don`t understand why as I did not have this problem before, but then I installed one premium theme and it all started. Now I have uninstalled this theme and wordpress, and installed it from beggining but the same problem even for the TwentyTen theme where there were never problems like this with standart font which has always taken latvian language.
Please please help! What could be wrong?
thank you!!!