Come on man, That's easy. The answer is on page 164 of the AKAI MPC2000xl Operator's Manual. Seriously, download the manual and read it from beginning to end to help you understand many things about the mpc2000xl and its operation and setup. You WILL find the answer to your question on page 164. You are asking too many obvious questions and you just need to take the time to read the manual (if you have not done so).
Type = ??? means the disk/drive isn't recognised. Of course you don't state what type of disk/drive you are using, so we can't be much more help other than to tell you to drive a different disk, or try formatting the one you have in your MPC.
USE the < Cursor > keys to change it back to the one you have Floppy? Dude, You better be making some fly beats cus you've vertualy asked "how do I turn this ish on" Personally, I respect your style and know you are cooking up the darkness. You should check out the Beat Battle section on here, I think that's the best way to learn how to operate a Mpc. 7.