I want to use the H2 via the USB connection as an audio interface for a computer, but the computer does not recognize the H2.
When you connect the H2 to the computer using a USB cable, the USB MODE SELECT screen appears, but the connection between H2 and computer is not yet in the online condition. Use the [REW]/[FF] keys to bring the cursor to "AUDIO I/F" and then press the [REC] key. At the screen that appears next, bring the cursor to "CONNECT" and then press the [REC] key again. When the indication "USB AUDIO I/F" appears, the H2 and the computer are in the online condition.
For details, see the section "Using the H2 as an audio interface" on pages 73 - 74 of the operation manual.