I'm not sure what you question is. If you're asking whether you can reuse the hard drive (1TB SATA) in the new build, the answer is yes you can. But if you're asking whether you can reuse the hard drive with the existing Windows 7 OS inside, the answer is no it probably won't work in my opinion and experience. The good news is that it won't "kill" the new build so you can just format the drive and install the OS after you backed up all of your data of course.
Edit: Just to make myself clear I meant to say that you won't be able to boot from your hard drive without formatting the drive first.