I've never heard of accounts being deactivated after long inactivity, so don't think that's the issue.
I don't know, but it might have something to do with adding Steam-purchased GW accounts to the NC master account, as I'm not sure if it's possible. Are there any reported instances of account-linking issues? You should try the ANet support forum that Mithran linked above me. I've heard NCSoft's support is very slow and not very helpful.
If the issue is you can't log into you're GW account, then the ANet support forums are definitely the right place to go to. Or you could try remembering the email adress you used to register GW with, and then use the 'lost password' function (GW should have that, iirc).