In doing some more research on your problem, I came across this Microsoft forum Q & A.
For Windows 7, .NET Framework 3.5 with SP1 is shipped with it as one of OS component.
For .NET Framework 3.5 with SP1, it includes .NET 2.0 with SP2 and .NET 3.0 with SP2 as prerequisite.
This means, (Windows 7) has the .NET Framework 2.0 SP2, 3.0 SP2 and 3.5 SP1 plus a few post 3.5 SP1 bug fixes on Windows 7. They are OS components. .NET 3.0 SP2 and 3.5 SP1 can be added or removed via the Programs and Features control panel.
Source: Cannot install .net 3.5 on windows 7
Since Windows 7 is supposed to have .NET Framework 3.5 included as part of the system files, you may want to run a System File Checker scan. SFC scans the integrity of all protected Windows 7 system files and replaces incorrect, corrupted, changed, or damaged versions with the correct versions if possible. SFC /SCANNOW Command - System File Checker
If SFC finds any problems, run the scan 3 more times as per the note in Option Two, Step 4. Perhaps SFC will fix a problem file and then allow you to install .NET Framework 4.