First step: Please confirm your keyboard settings.
It happened once to me, from one version to the other the naming
convention for Latinamerica Spanish keyboard settings had changed from
"LA" to "LATAM" - and unknowingly (unsuccesffully) is was trying to
log in using a "Laos" keyboard setting. It took me a couple of weeks
to find that out and solve it changing the conf file in terminal mode.

Disregard if your username looks ok and your password does not contain
any strange character.

The only thing I could come up with is check your caps.

Would the screen resolution have anything to do with it not signing in?

Do you have your numlock key on? It is not on by default.

I installed ubuntu last night, it allows me to type my user name and
password. When I hit enter it takes me back to the same sign in
screen, the only way to get in is failsafe mode. I want to get in the
regular way, what can I do? I have installed twice, and username and
password are correct, same thing again...

Remember when your logging on, it is case sensitive. That is the only
thing that I could possibly think you are having.