Steam can't find my account, offline data deleted, now what?

Steam for Mac refuses to log me in and it thinks my account does not exist. What can I do to fix this? I was in offline mode for a while, but now I'm getting errors when trying to log in or recover my account.

Edit:

I reinstalled, nothing doing. I contacted steam. Now I suppose I wait. While waiting, I am wondering if playing "The Heist" could have trashed my account. At the end, they ask you to create a Steam account. It seems like that might have overwritten or trashed my old account. Does that sound plausible?

Solution 1:

Try to log in at steampowered.com so you can see whether it's a client or login data issue. Also make sure you don't use your community profile name instead of the username (they can be different, it took me a while to remember that after not having used steam for a while).

If you also cannot login there, follow theses instructions from steam, basically it means installing the client again (as you intended to do anyway) and selecting I don't know my account name (it will be emailed to your registered address) or I know my account name if you are certain about it (asking for the answer of the secret question).

If this still fails, contact support.