Change the browser to a better one, like Firefox, or Opera...
I had the same problem long time ago with IE, it didn't display any polish diacritics, or sometimes display some of them, and even somtimes worked well. It was impossible to solve this problem neither by reinstalling IE, nor by manipulating with settings/fonts. The problem appeared abruptly, without any logical reason, no new software was installed, just switched off the computer for night and next day... surprise.
Or maybe try gmail in english.