To perform a clean installation:

: It patches or removes key system files, such as slwga.dll , effectively preventing Windows from running its "Genuine Advantage" checks.

Windows 7, released in 2009, is widely regarded as one of Microsoft’s most successful operating systems, praised for its stability and user-friendly interface compared to its predecessor, Windows Vista. However, its success was accompanied by a persistent cat-and-mouse game between Microsoft’s security developers and software pirates. Central to this conflict was and the controversial community-developed tool known as RemoveWAT . The Purpose of WAT

Note: This "rearms" the grace period. You can typically only do this 3 times. Method 3: Disable the WAT Service