Downgrading to Windows 7 Error

Hey all :)

I recently bought a PC on behalf of work, believing it to be Windows 7 and it turned out to be Windows 8. A bit annoyed, I ordered a Windows 7 Professional disc and am now trying to downgrade the PC. However, after pressing 'Install Now' on the installation Window and selecting 'Update the files now', I receive the error:

"Windows could not update the installation files. To install Windows, close Setup and restart the installation. Error code 0x0".

I did a Google search to see if I could fix this error, or if anyone had any errors like it, and I came across this:
http://answers.microsoft.com/en-us/w...a-3eb2f78d1c1f

I've uninstalled all of the security software on the PC, made sure the PC was updated fully, and also tried checking the hard drive with chkdsk. However, when trying this, the computer got stuck at 27% for over half an hour, and I Googled that as well and found out that there could be a problem with the hard drive, even though it's a brand new PC fresh out of the box. Windows 8 runs perfectly, but I really need Windows 7 to comply with everything else in the office.