If you're looking to use Windows 8.1 Pro, there are legal ways to obtain it:
Cracked operating system installers are a favorite vector for cybercriminals. Common payloads include: Windows 8.1 Pro Iso Download With Crack
After downloading a genuine ISO:
If the original PC is discarded, you may transfer an OEM license only if it was a "Full" (retail) version. OEM keys locked to specific motherboards generally cannot be transferred. If you're looking to use Windows 8