Fast and simple checklist:
1. Checked so the cable is seated propperly?
2. Is the floppy cable the right way arround? (If not floppy led usualy lighs up constant.)
3. Is the floppy placed on the correct floppy cable header? (If only 1 drive you should use the last cable header.)
4. Readhead dirty? (Read below)
Many floppy errors such as unknown disks or simple intermittent read errors can often be solved by cleaning the floppy readhead with some alcohol and a q-tip.
