Hi,
Unfortunately, I have no idea what happened to your account. Are all your old posts still there, showing up with 'Guest' as the username?
Generally, inactive accounts with very few posts which are dormant are subject to removal. To give you some examples, an account with 0 posts may be removed if that account has not been used for more than a year. If an account has gone dormant for several years and there are fewer than 10 posts, the account might be removed, but only if there is not much content to the posts. If an account has more than 10 posts, it would only be removed by mistake.
When an account is removed, the posts are retained with very few exceptions. Examples of exceptions would include something like a question which was never answered or a topic which was timely (example "I'm going to the AMA Vintage Motorcycle Days in Ohio in 2010, who is going to be there?").
If we get a request from a member to remove an account, the account is removed no matter the post number, but the posts are retained unless the member explicitly requests that they be removed. Even in a case like that, I will favor scrubbing any personally identifiable information rather than remove good technical content.
Do you fall into any of those categories? In case you are thinking about asking, unfortunately, there is no really good way to re-associate existing posts with a new account.