chemist

I purchased a refurbished(I assume) Quantum ELS85S from Hard Drives USA for several old Mac LC520s that I use in the teaching profession. I know these are obsolete but they are easy to use in my situation. When I first hooked it up it wouldn't get recognized. I tried it a couple of more times, taking it out and putting it back in, and it finally was recognized. I loaded 7.5.1(I know, don't laugh too hard) and it worked. I loaded a bunch of files and it worked perfectly. I removed it to put a 50 pin IBM drive that I've had for several years to retrieve some more files to load on the new Quantum. I hooked the Quantum back up and since then my computer and other 520s I have won't recognize the drive. It's like it's not there. Says there is no SCSI device using Norton tools. I get a small mac icon with a question mark on startup. The company says there is nothing wrong with my drive and I don't know what I'm doing. I had assumed it didn't work the first time due to a bad pin connection. I have tried different connectors, computers, etc. but it still won't get recognized. I hear the drive start spinning on startup, then it stops. The IBM works everytime though. Would anyone have any suggestions? If I send it back and they test it good, they will charge me 25% restocking fee and send another one(no refunds).
Also, I have several old Quantum drives that display the same problems. I have read they just get old, the bearings go bad, etc. Is there anyway to revive these old drives that give the question mark icon on startup? Much thanks to anyone who can address this.