More a reminder note for myself than anything... I always - always - run into this problem when I'm trying to uninstall SQL Server. The installer runs some checks on a screen saying "Setup Support Checks" and always fails the check labeled "Restart Computer."

I always end up Googling for the answer and it's always the same (and it always works):

Go to the HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\PendingFileRenameOperations key in the registry and clear it out.

Once that's done, run the installer again and the check will pass. Done and done.