If you connect the Drumit5 to your PC via USB and power up the Unit then press the USB button, do you see the DRUMIT5 as a drive on your PC? if so you need to format it by right clicking and choosing format, then make sure it's formatted in the way specified...
FAT32, 32 kbyte clusterObviously anything that is already on your drive will be over-written, so if you can, copy the contents off it to your PC before formatting. Format, then copy back over.
FAT32 refers to the type of File Allocation Table and is how hard drives are formatted -
http://en.wikipedia.org/wiki/File_Allocation_Table I don't know if you should contact your distributor or whether this invalidate any warranty, I don't think it would...