The procedure depends on what version you have.
Below there is the procedure for 20 GB , on other models procedure is the same, but you must find the right download for your model.
For 20 GB :
TO RESTORE "SYSTEM FILES MISSING" LOCKED PLAYER
--- This applies ONLY to the 20 gig version of the H10! ---
--- This procedure formats your H10 so all data will be erased on the player! ---
1. Power off H10 - 20gig unit.
2. Insert staple or other small object into reset hole to press reset button.
3. Connect player to USB cable.
3. Hold down Select key (labeled "O" - right button on front of player) while also holding down power key until player boots.
4. Unit must display "Emergency Connection."
5. Unit will now appear as a drive under My Computer. Right click on
drive, select Format. No need to change anything, just proceed.
6. Download H10_20GB_System.exe. It is a self-extracting archive. Double click on it and unzip to c:\iriver.
7. Locate iriver directory, double click. You will see H10. Double click once again; you will see System.
8. Right click on system, select "Send to" and choose the directory of the player.
from System Files Missing
If you have the 5 or 6 GB see iriver - H10 5/6 GB Series Support