A browser is what you use to search the internet. Yours might be Internet Explorer, Firefox, Safari....
You can find out what version by going to the Help menu on the top of your window and clicking on About
In order to be logged in you would have had to register on our website at some point since April 2008. If you were checking out as a guest then you were not logged in.
For example: Have you recently updated security on your site? Do you have cookies disabled? Are you using a very old computer? Any problems on other sites, anything unique that you noticed?