Hi zippy, what operating system are you using - is it XP or something like Windows 95? As a Director of a EU project I had to give away (yes true, that's where your taxes go!) 85 computers to various small engineering firms in an Objective 1 area. That was the easy bit, Windows Passwords then became an absolute nightmare for us - there is a lot of help out there, but in the end on three machines I had to re-install the operating system! I gather that Windows 98 was better, but that Windows ME was equally obstinate!
As I write this, another penny begins to dawn - are there differences between passwords now on ebay.com and say ebay.co.uk - one used to do both. Are you signing on to the correct country with AS?
More to the point, if you have tried all the obvious things, then it looks like it may be something AS may have come across it before - tell support about the steps you have taken and simply ask their advice.