First of all, you should get the Rockbox manual so you have it to consult.
http://www.rockbox.org/manual.shtml
You probably still have original Sansa firmware on there and can still boot into it. Try turning it off and holding down the left (<) button as you turn it on.
http://download.rockbox.org/daily/manual/rockbox-sansaclipplus/rockbox-buildch3.html#x5-280003.1.3
If that gets you to the original Sansa firmware, good.
The Sansa Updater is not necessary. You should uninstall it from your computer.
Look at the Firmware thread near the top of the page and search for “manual installation.” Basically you download a zipped file, unzip it on your computer and drag the unzipped file or folder (I forget) onto the driveletter of the Sansa . (If your Sansa shows up as E: SANSA FUZE, then just copy the unzipped stuff onto E:). Disconnect and the firmware will get intstalled.
Here’s how to uninstall Rockbox:
http://download.rockbox.org/daily/manual/rockbox-sansaclipplus/rockbox-buildch2.html#x4-210002.5.1
