I absolutely dread re-installing .NET in Windows 7. Luckily, I would like to share a new workflow that may make it easier so that you don't need to 'reinstall' your entire operating system.
1. Click Start > Control Panel > Programs > Uninstall a Program.
2. Find and highlight Microsoft .NET Framework 4 Client Profile > Uninstall > Repair > Next.
3. When it prompts to restart, click Restart Later.
4. Repeat for the Microsoft .NET Framework 4 Extended.
5. Reboot the machine.
Thanks to Dwayne Poot for this tip.