Ok if the disk is new and you cant save or load samples the diskdrive is maybe dirty or broken. I you're familiar with electronics open the case of the S900, unscrew the powersupply (the disk drive is under the powersupply).
you need to dismantle all the cables there.
Oh I forgot something.
Before you open the case unscrew the 4 screws on the bottom of the sampler that hold the disk drive. Its better when you place the sampler on the table like this http://img153.imagevenue.com/img.php...122_1084lo.JPG
cause otherwise the screws fall in the machine and....
Ok now you can take the diskdrive and open it. Is it dirty? clean it. But please BE CAREFUL !!!!!!
If it is clean you have a more serious problem cause there are not so many diskdrives that fit in the s900. There is a company that sells drives for the s900 but they want 80$ or so. You can go with an Amiga 500 Drive but it has no frontpanel and if it has the panel it still dont fill out the hole for the disk drive cause the original drive has the doulble hight.
I hope your drive is just dirty.