Hi, it seems Ensoniq keyboards do strange things when the connectors don't contact firmly. I read some articles reciping a cleaning of the pins and use of a contact cleaner spray.
If the fail happened when changing the disks, it could be that the last disk's door didn't shut apropiately touching the floppy arm. So you have it miscalibrated. Try with another OS disk first. If the floppy is faulty I think spares are difficult to find. Look in the Rubber Chicken web for details about a firm that repairs floppies. I have too, some old Transoniq Hacker articles where somebody found a replacement drive, in case you wonder wich brand/model are suitables.

If you want to use a Hard disk, you'll need the OS floppy at any time... and you should format your hard disk before in a PC, or have formatted and OS installed in another EPS16.
Hope this helps