Sansa Clip won't delete files or accept firmware update

This is not good news, if you can’t format any which way.  Can you run a Windows chkdsk (error correction) on the Clip drive?  (Right click on it, Properties, Tools, Error-checking.)  Also, maybe (I’m totally guessing) the firmware has become corrupt, and it would help to reapply the firmware (see the firmware upgrade sticky thread at the top of the forum).