Problem with logins, who's online, and cookies

I was working with the dev version of e-Commerce the other night and crashed my entire site. Since then I have been getting weird behavior out of the login and who's online modules.

Some people can't log out, some say they had to try several times to log in, some say they are listed 2-3 times in the who's online when logging in for the second or third time of the day, as though they never logged out, and I personally cannot see people who are online that I KNOW are online, it just says Who's Online: admin + 1 guest etc...

Somewhere I think in one of the Drupal versions, there was an area to change the name of your site cookies (may have been my test D6 site). Does anyone know if this is still in 5.7 and where I can find it? I have looked everywhere.

Secondly, does anyone think changing the name of the cookie might fix the above problems?

Thanks in advance!