@Flying: I hear you and have been there myself at times :( I think Amazon have a "problem" in that second hand units should have a Wake Screen that warns "Device LOCKED" or something so that potential innocent buyers do not buy in good faith and find themselves in the position yourself and I am sure many, many others are put into :( I think it's something they just never thought about, which is a pity.
I have to wave a small red flag and warn that I had the same problem when buying from a reputable high street re-sale store. All looked good but the thing was a brick.
Small green flag - the WAREHOUSE page on Amazon often lists refurbished Fires and Kindles, sometimes at very respectable discounts. "refurbished" means full warranty from Amazon so it may be a suitable "middle ground" between new and second hand?
Just to sign off with this and thank you CW I thought I had cracked it by plugging it into my lap top. It was recognised and I was able to drag and drop my kindle books and music onto the device. Ummm but of course though they are in the Kindle I still can not access them... I bet one day the previous owner will remove it so I will keep trying just for the hell of it.. all best to you.