What is the best way to buy windows 7 product key cheap or free?

Using a free Windows 7 product key, even if obtained through a method like retrieving it from the BIOS, comes with several serious disadvantages:

• The most significant risk is that the key is invalid or has already been used.  A key that's not legitimate will likely fail to activate Windows 7.  You might get a temporary activation, but it will eventually expire or fail.
• This can lead to a system that doesn't function properly.
  Sites offering "free" product keys often contain malware or viruses. Downloading and using the key could compromise your system's security, leading to data loss, identity theft, or other serious problems.
• Using an invalid or stolen Windows 7 product key is a violation of the Microsoft software license agreement.  This can lead to legal issues, including fines or lawsuits.
• If you encounter problems with Windows 7, you won't have access to legitimate technical support, as Microsoft doesn't support pirated or unauthorized copies.
• Windows 7 is no longer supported by Microsoft.  Without a valid product key, you won't receive security updates, which leaves your system vulnerable to malware and exploits.
• A non-genuine version of Windows can cause unpredictable behavior and instability, leading to crashes, slowdowns, and other problems.
• Some features of Windows 7 might be disabled or restricted with an invalid key.

While the temptation of a free Windows 7 product key might seem appealing, the risks and potential negative consequences outweigh any perceived savings.  It's much safer and more reliable to obtain a legitimate copy of Windows 7 if you need it.