If you've run Windows Restore, going back to a date when your system was supposedly clean, that alone can and often will cause your antivirus to malfunction. Antivirus programs rely heavily on correct date and time and since System Restore takes the system back in time there'll easily be conflicting time stamps. Usually that means you'd have to totally clean the program of your system and either reinstall it or replace it with some other antivirus. For Eset, the manual uninstall instructions and link to the uninstaller program are here:
http://kb.eset.com/esetkb/index?page=content&id=SOLN2289.
Of course the best solution after a virus attack is always to do a clean install of the entire operating system (of course after saving your photos and other irreplaceable data), but if that is out of the question, there's a bunch of other things you can do.
First things first: Was that a virus or simply an aggressive marketing program you got? What were the symptoms? Marketing programs can be quite persistent, but they seldom break anything. As they're not actually viruses, most antivirus programs won't necessarily notice them. Eset has a check box for PUA (potentially unwanted applications) leaving it up to you either welcome adware as a consumer aid or consider them as malware. What was your choice?
If you got a "real" virus, a bootable virus cleaner is what you need. Something like
F-Secure Rescue CD or
Kaspersky Rescue Disk should do the trick. There's a lot more of them, these two are what I've been using. See
https://www.raymond.cc/blog/13-antivirus-rescue-cds-software-compared-in-search-for-the-best-rescue-disk/ for alternatives. You can also get an antivirus scanner to boot from an USB stick, google for "bootable virus scanner usb".
After having cleaned your system from outside with one or more bootable scanners, start cleaning from within Windows. At first reset all of your Internet browsers including Internet Explorer. Then get some cleaners. Start with RKill to stop any malware running:
http://www.bleepingcomputer.com/download/rkill/. From the download site you'll also find links to AdwCleaner and Junkware Removal Tool, both of which are quite fast. ComboFix makes a more thorough job, the best part being that it can fix many settings changed by malware. Another great tool is Malwarebytes' Anti-Malware,
https://www.malwarebytes.org/mwb-download/ which I recommend running in any case.
Last but not least, if every cleaner says your system should be clean and you've double checked your browsers' start pages and add-ons but you still find yourself on a marketing search site, right click the icons for every browser in every location and choose "Properties". On the Icon tab, Target window it should only read "C:\Program Files (x86)\<YourBrowser>\<yourbrowser>.exe". If you find any net address after the last quotation mark, simply remove it.
Good luck!
