Dan, did you make a computer backup of your SD90 prior to this happening. If you did, all is not lost.
I think you need to format the user drive from within the SD90 and then reinstall your files from your computer.
If you did'nt keep a backup then I think you have a problem.
However, do not take my advice straight away, see if another player has better information than I have given you.
Hope all goes well.
Alan