Hmm,
Its Sophos causing the issue.
- Click Start or use the Windows + R to open the Run... box.
- Type in the following, then click OK:
services.msc
- Locate the service called Windows Search, then click the Stop icon on the top action bar.
- Once stopped, perform another uninstall (as required).
- If the problem has been resolved Start the service again so as not to lose the indexing facility.
Once Done then try to install Symantec again.