If your system is a laptop you might have a hard time attaching the hard drive as a secondary drive to a working system - which I'm sure you have a working system laying around, right?
Maybe if you tell us more about your system you will get some other ideas that might be easier:
What is your system make and model?
If a Dell, what is the Service Tag number?
If an HP what is the serial number?
What is the installed Windows Edition (Home, Pro, etc.) and Service Pack?
Does the system have a working CD/DVD drive?
Do you have a genuine bootable Windows 7 installation CD that matches your installed Windows Edition and Service Pack?
If the system used to work what do you think happened to it since the last time the system worked properly?
When you attempted to repair the system and "it couldn't be fixed" is that what the message said or did it say something else?
What happens when you attempt to start Windows normally?
Having never used FRST and if you did how were you able to do that if the system does not boot?