a different account shows up when I sign in

I have an account that I use only for personal stuff (acct. 1) that I've been using for months. Recently I created another account (acct 2) because I needed it to share info with business associates. The accounts have separate names, separate email addresses, and separate passwords.

The problem is that now, when I try to log in to my personal account (1), the other one comes up. I've tried resetting Safari (clearing cache, history, cookies, etc), rebooting the computer, etc., and nothing has worked. I'm assuming it's using IP addresses, but if I log in with separate account info, it should take that....lots of people share computers. I talked to a couple of friends who use multiple Skitch accounts on the same computer, and they don't have issues.

Please help!!