Hello, i have some questions . I just have installed 3.2 version, everything is fine, but, where i can find my USB drive menu button? And why when im uploaded *.mkv file, and click to play it, its loading about 2 hours and nothing?

You can find info on enabling the USB port here:

MKV files are virtually not supported on the Apple TV. 480p and under will play, but the Apple TV itself is not powerful enough to play anything higher.