Download the following two programmes to your desktop :
1.
Rufus For 64bit systems 2. Windows 7 64bit RC I will PM the link for this
Insert the USB stick Then run Rufus
Select the ISO file on the desktop via the ISO icon.
Press Start Burn
Insert the USB into the sick computer and start the computer. First ensuring that the system is set to boot from USB
Note: If you are not sure how to do that follow the instructions
Here Windows 7 and Vista screenshots When you reboot you will see this.
Click repair my computer Select your operating system Select Command prompt At the command prompt type the following :
sfc /scannow /offbootdir=c:\ /offwindir=c:\windowsThis will verify all windows files required for start