I've had an E585 for the past 18 months that's locked to the 3 network and which has worked flawlessly. Last week I bought a secondhand E585 (also locked to 3) along with a new 3GB SIM for a work colleague. However, I've tried everything I can think of but just can't get it to connect. I've been running both units side-by-side and, where mine connects with no problems and usually excellent signal strength, this other one just does one of three things:

1. It does several minutes of searching then reverts to "No Network"
2. After a long search it eventually connects to the 3 network then constantly cycles between "Connecting" and "Connected" eventually reverting to "No Network"
3. It eventually connects to the 3 network and stays connected but only until I try to connect one of my WiFi devices to it, whereupon it immediately goes back to either doing (1) or (2) above.

I've reset it to factory default (many times!), checked the APN settings and the firmware (it has the latest version, same as my own) as well as reinstalling the firmware using the links in this forum. I also swapped SIMs between units - the SIM from the problem unit works fine in my own but the SIM from my own doesn't make any difference to the problem unit, it still fails.

I've been to half-a-dozen different places across the UK on my travels in the past week and my faithful old unit has worked like a charm in all of them but this other one has failed everywhere. Well, there was one place - Peartree Park & Ride car park in Oxford where I managed for a few short minutes to get connected and, to my amazement, a speed test registered 6.5Mbps! But as soon as I left it disconnected and hasn't worked since.

I've been in contact with the private seller who seems quite genuine and apologetic, even though he says it always worked well for him and he only sold it as he's changed jobs. He's offered me a full refund but I said I'd give it one more try before that. I've not yet contacted 3 customer support as, judging by the comments in this forum and from other things I've heard, they sound pretty ineffectual and I thought that I'd get much better advice from here.

Has anyone had a similar experience and/or have any advice as to what I can do? Any help would be really appreciated as I'm completely out of ideas!