Hello and welcome.
Initially, it sounds like the hard drive may be full. Did you install it after downloading?
You could try starting up while holding the Space Bar...that will startup in Safe Mode, which bypasses a lot of Login Items and other non-essential files. If that is succussful, see how much free space is left on the drive. If it is less than a GB or two, then OS X doesn't have enough free space to startup and run properly.
C