Problems with clean install onto SSD

Hi,

Hoping someone can help, or point me in the right direction.

I have a 2009 Mac Pro I inherited a while ago. In a bid to improve performance I decided to install a 120GB SSD for the boot drive. Initially this worked fine. I loaded all the system files and applications onto the SSD and everything else onto a separate hard drive. This worked fine for a while and really sped things up, but today things went pear-shaped.

This morning I booted up fine, no problems. Except no apps seemed to open. As an example, I'd open Safari and it would be registered as being open, but there'd be no window. This happened for pretty much everything. I checked permissions and there seemed to be a tone of errors, so I tried repairing them but the progress bar just hung halfway through. As everything hung, I decided to force shut down.

When I then went to boot, I ended up with the grey padlock and password field for the firmware password (that I don't know). After suggestions that this might require a PRAM reset I decided to do just that. It went through the motions and got me back to the login screen, but when I tried to login my admin password was rejected. I was told I couldn't login to this account at this time because of an error, totally locked out. This remains the case.

Eventually I decided to just do a clean install from USB (to be honest I've always been a little unsure whether I set the SSD up correctly in the first place, despite it working okay), so I used another mac to create a Mavericks install ISO. Now, however, when I try to get to startup manager to start the install all I get is the option to boot, which just takes me back to the login screen, which I still can't get beyond.

I don't claim to be great at any of this, and I'm totally prepared to accept I've ballsed something up along the way, so any suggestions would be great.

Thanks!

F