New hard drive in early unibody 2011 MacBook Pro won't boot... Please help!

Newbie here!

I just replaced the hard drive (to a 1T senate SATA) in my MacBook Pro and upgraded the RAM from 2, 2GB cards to 2, 8GB cards.

Hardware install went smooth, backed up old drive to time machine & made a USB of OSX for install on new drive.

I've gone in and reformatted the new drive with the proper settings (1 partition, journaled, etc...).

When I go in to boot up the system, the computer goes to apple logo grey screen and the loading bar comes up, loads to exactly the halfway point in about 6 minutes, then just sits there... For hours.

I've tried it many times always with the same outcome.

I need my computer for school TODAY! Please help!

Thanks!