Things like Adblock and Scriptblocker prevent things from being run without your consent, but as UrQuan has said, it sounds like your computer is already infected with some sort of malware. In which case, installing new preventive measures might only hide the problem rather than fixing it properly. You're going to need to run all your usual virus and malware scans. Personally, Malwarebytes antimalware
is my go-to program for scanning (not necessarily removing) but there are certainly plenty of others. You'll probably also want to do your homework and find out what you can about your specific issue/infection. Tech support forums are your best bet here because they are going to be filled with other people just trying to deal with a problem. Geekstogo.com
is a great place for help. It's just other users, some with extensive technical knowledge, some are just hobbyists, some are just random people looking for help.
Run your antivirus scans and if your programs allow you to quarantine or delete things, do it.
Then restart your computer and go into Safe Mode (I'm assuming you're using a Windows OS) and run all the scans again and quarantine things that still come up.
If you are comfortable with manually locating and deleting files or editing registry keys, do so. If you aren't, make sure you do a good deal of research and find step by step instructions specific to deal with whatever bit of malware you're dealing with before modifying or deleting anything manually.
Restart normally and do another sweep of scans. If the problems persist, go back to Safe Mode to continue scanning and dealing with malicious files.
It can sometimes be a bit of an exercise in frustration tracking things down and finally squishing them, so try to stay calm and be patient.