I want to trademark a name (it used to be the screen name/email address of a loved one) and use to it as the name of my new business.
I have searched the name in USPTO and it has not been trademarked by anyone else.
However, when I google search the screenname (its a play on words) I see that several other people are now using it as their usenames for Twitter, Tumblr, etc. Could this prevent me from trademarking the name?
Also, I have no interest in stopping or making people change their twitter and other social media usernames, as long as they do not use it for business. If trademarked, would they no longer be able to use the name?

