iPhone suddenly asking to connect to iTunes

Firstly the problem is with 2 iPhone 4's. Both are not barred or blocked. Both were working fine after repair.

Let me make this a little simpler as its quite complicated in my own head!

iPhone A was a tethered jail broken phone I bought from eBay. I accidentally turned it on without it being charged (which as its tetherd I'm not meant to do). It then asked to connect to iTunes and since then has not restored. Even in dfu mode. Then suddenly a month after being stored away in my drawer I pulled it out, turned it on, and it worked without asking to connect to iTunes! Great I thought! I used it for a week without the jailbreak and then the battery died on me. I plugged in my charger to put some power into it and there it was again. Connect to to iTunes. This phone underwent repair and has slight water damage but I cleaned it out with isopropyl alcohol 99.9%.

Anyway, iPhone B is another phone I got from eBay. It had a faulty lock button which I fixed instantly, and from then on was working perfectly. To cut the chase after a moths use I got the connect to iTunes problem. Won't restore even in dfu mode. iPhone B has never been jail broken and has no water damage.

I've switched ports, downloaded latest iTunes. I've even used different USB cabled but no luck.

I've done many hardware repairs in the past but if I damaged something I'm not sure, everything seems ok to me, even with moderate use for a while surely an error would have Coe sooner if it was a hardware fault?

Both phones have the same error message on iTunes.

'there is a problem with your iPhone. The iPhone you connected may be damaged and cannot be activated for service. We recommend you visit your nearest apple store for more information'

Amy help on this matter would be greatly appreciated