As I own one of these and have had lots of fun with it, I can give you a hand.
First, you'll need to do to replace the missing OF files. Download the iriver MTP updater from
here. Connect your H10 in UMS mode by holding the select (O) button down with the USB cable plugged in while powering the device on, then run the application found in that .zip file and tell it where you got your device from, and follow the on-screen instructions to restore it.
Second, once the device had been restored to working order, reset it by using a thin pointed object to press the reset button in the little hole at the top, then reconnect it in UMS mode again. There are two ways of getting Rockbox installed on your device, I myself prefer the manual way, however, it's easier to use
RBUtil. Download that application and run it. You may need to tell it which drive if your H10 if it can't detect it automatically. The interface -should- be easy enough to follow, however, as I don't use it myself, I can't tell you exactly what to do.
I hope this helps!