My computer has two drives, both 1 TB. One has Win7 already, and was listed by the Win7 disk as primary. The other drive, which has an older Win on it, I wanted to be wiped. It was listed by the win7 disk as system. Because I could find no other convenient alternative to formatting (using disk manager didnt work, i would get an error JUST saying it could not be done), I booted off a usb drive containing win7 iso. From using the win7 setup, I selected the hard drive that I wanted to format, and went advanced driver options and selected format. Afterwards, the hard drive that I wanted clean was listed as having full spaces available, while my main drive was unchanged in spaces available. I quit out of win7 setup, and restarted, but the system would not boot from my main drive. Even removing my supposed wiped drive would not allow me to boot from my main drive. It was not a boot priority issue, it simply would not boot. What happened, and what can I do EDIT: To check the status of my main drive, I installed win7 onto the new drive which I formatted. Booting up, I can see that my main drive that is unbootable still retains ALL of its files functional. However, it just cannot boot from it. EDIT2: I have been told that in my case, the dual boot setup meant that my old windows hard drive held critical information for booting and operating my win7 hard drive. If this is the case, what can I do?