Computer security scan

I'm running Avira, Windows Defender and Malwarebytes of which I have ran several scans,even in safe mode and neither have detected anything.This has been happening off and on for several weeks but as of late its gotten worse. I went back as far as i could go to a restore point but that didnt help either because on Windows Vista I can only go back a week, also deleted cookies.When the grandchildren come over they use the computer and who knows what sites they go on!

Sometimes silence is golden,sometimes it's not.