Borrowed this from another post...not sure if it works on a Cicso RNG 200 though (these may be the same steps you already took)
1. Turn the STB off
2. Press and hold pause for 15 sec. > You will see a flashing message light/envelope in the LED display panel after 15 secs.
3. Press the Page Down button -> You will see E-00 in the LED display panel.
4. Press List or my DVR button 3 times hddf appears.
5. The formatting will automatically begin.
6. The formatting will take 2~3 minutes after which the box will power cycle automatically. The hard drive is now formatted
CAUTION: This will erase everything on the hard drive
EDIT: added source: »Re: Reformat Comcast Explorer 8300HD with I-Guide?