I think this is not an install but rather that you've made a live USB You should not be prompted for user - password I guess you've made a mistake somewhere (and I don't have the time to walk you through this)
Don't fix it if it ain't broken, don't break it if you can't fix it
I believe that for the LiveCD, the username is 'mint' and the password is blank. However, when you run the LiveCD you aren't generally prompted for this at any point, so if the LiveUSB is meant to work like the LiveCD, you shouldn't have to enter the username. If that doesn't work, then I would guess that you did a regular install to a USB, which would mean that the name and password were entered during install at some point. One way to check the username would be to see if there's a /home directory on the USB, and see what the name of any subfolder of /home is.
Mint is the username, and there is no password. Thanks eStyleS Husse, yeah youre right, i just made a live USB Its odd, on one of my pc's it asks for the login, but not on the others.... Well, it all works dandy i'm happy. Thanks guys!