Because the problem appears to be malware related, in some situations, I've needed to run removal tools from ALL of the various user profiles to clean things up.. It's a pain to run all those scans, but because each user has their own registry, of sorts, it frequently involves running the scan tools from each user's login.. And yes, "unhide.exe" may be needed in each user as well..

If that doesn't work, you may need to run a repair install, or possibly a complete format and reinstall, if the system files are too badly damaged.

And after all of this troubleshooting, if it still doesn't work, yep, replacing the hard drive is the next best step.

Hope this helps.