GOA changed everyones account passwords on 27th August 2003 due to being hacked. They changed both the game and the subscription passwords. There were emails sent out at this time. I know the exact date because I saved my email with the new details. So, check back through your old emails if you still have them. If you haven't tried to log in since then this is probably the reason you can't now.
I managed to log on to my EU account and all my characters are still there. Made me realise they aren't as good as I seem to remember. Toons I thought were fully TOA'd are only ML8, toons I thought were high realm rank are only RR3 or 4 (highest is my old Hero at 6L6). I have more plats on Ywain, even after buying a house and doing templates, than all my toons put together on Prydwen. So if you can't get access to your old toons I wouldn't worry, you arent missing much other than a bit of nostalgia.
If Mythic offer some form of free transfer I will migrate a few of my toons over. But nothing is ever free is it, greedy games companies always want to grab money for moving toons between accounts (its one of the biggest ripoffs in the MMO industry, charging up to a months subs for a simple database transfer that is automated and takes a few seconds). So unless it is free or the charge is a nominal one, I probably won't bother, or at very most I will pile all my plats and useful items onto one single toon and transfer that.