your hard drive is prolly dead. It is over 20 years old. Load the disk (the disk loads the OS and samples), then clear the sample memory (Press Master - 4) and you good to go.
Basically the way it works is you activate a "module" then you press a number to select one of the options of that module.
To sample, you go into the sample module, set all your options, set a key range (if not the sample will be mapped from C1 to B1, centered at G1, then your second sample will be C2-B2 centered at G2, and so on) press 6 for threshold sampling, or 7 for instant sampling, then press 8 to stop. Soon as you stop, you can hear your new sample from your keyboard or MPC. Once you set all your options, they will be the same for every sample unless you change them, obviously except for "Place Sample" where you set the keyrange.
Go into the Digital Processing module to truncate or loop, etc. (you gotta specify what sample to truncate by playing it from a MIDI keyboard or your MPC's pads)
For the level, filter and envelopes, go into the Analog Processing module (you gotta select your sample again from your MIDi keyboard or MPC) and then press the numerical buttons for whatever option you want. Also while you're in here you can set the separate outs for each sample if you want.
There is a program called EMXP that you can use to transfer samples between the EMAX and your PC it shere:
http://users.skynet.be/emxp/ I use it to save my samples on the computer, and to load drum sounds from my PC into the EMAX. With floppies, you gotta use DSDD, just like the 60 and 950, and you GOTTA FORMAT A FLOPPY BEFORE YOU BEGIN SAMPLING. FORMATTING A FLOPPY WIPES OUT THE EMAX MEMORY. Learn from my mistake dude!!! lol
That should get you started. I paid $250 for my mint condition emax rack a year ago and it was just regular no SE and no HD, and I had sold it just recently for the same price. It got damaged and the buyer returned it so now I'm trying to fix it and once I do I'm keeping it. So your price ain't too far off, as long as the HD is working and its in very good physical condition. But if I was you I would keep it. I bought an S900 at the same time as the EMAX, and I ended up selling the S900 because the EMAX was easier to use and better sounding IMO, especially the filters.