A clean scan and a misbehaving PC can both be true at once. The behaviour is data - it is pointing at something, and the job is to find out whether that something is malware, a hijacked browser, or a dying hard disk wearing a virus costume.
This is the most frustrating result in antivirus work: Quick Heal says clean, the PC disagrees. Pop-ups keep coming, the browser lands on strange pages, fans roar at idle, or everything is suddenly slow. None of that automatically means the antivirus failed. This page works the honest ladder: first separate the browser-only problems that no antivirus scan will ever see, then the second-opinion scan done correctly, then the non-virus causes that imitate infection perfectly, and finally the threshold where reinstalling Windows is not defeat - it is the diagnosis arriving.
Close the browser completely. If every symptom stops, your problem lives in the browser, not in Windows - and no full-system antivirus scan will find it, because technically nothing in the system is infected. Browser problems have their own fixes: remove extensions you do not recognise, reset the browser's settings to default, clear the notification permissions that scam sites tricked you into allowing (the usual source of desktop pop-ups that look like antivirus warnings), and check the browser shortcut has not had a web address glued onto its target. A web page also cannot scan your PC - the full-screen virus warning with a phone number is a scam page, and closing the tab is the entire fix.
If symptoms are system-wide, a second opinion is reasonable: a dedicated on-demand scanner from another reputable vendor, run as a scan only. The discipline matters more than the brand: it must be a scanner, not a second resident antivirus. Download it from its official site, update it, run its deepest scan, and remove it afterwards if it asks to install real-time protection. Two real-time engines together will cause the exact slowness and conflict you are trying to diagnose. If Quick Heal and a reputable second opinion both say clean while behaviour continues, believe the pattern: the cause is probably not a virus at all.
Check the drive's health and free space before the third scanner, not after. Technicians find hardware at the bottom of a surprising number of virus hunts.
Some signs should not be talked out of existence: new user accounts you did not create, security settings that switch back after you change them, Quick Heal or Windows Security being disabled by something, unknown remote-access tools installed, or files being renamed with strange extensions - that last one is ransomware territory, where the correct move is to disconnect the PC from the network and any connected drives immediately and get professional help, not to experiment. If money has left an account or work data is involved, treat it as an incident, not a home repair project.
If the browser is reset, two scanners say clean, the hardware checks out, and the PC is still wrong in ways nobody can name - or the opposite: every test says the system files themselves are damaged - then the honest endpoint is a clean Windows reinstall. This is not an admission that antivirus failed; it is recognising that some states cannot be proven clean, and an unprovable PC should not hold your banking. Back up documents and media only, reinstall, put Quick Heal on from the official site before your data returns, and scan the data as it comes back. Most people who finally do this say the same thing: they wish they had done it a week earlier.
See the Quick Heal download, installation and scan process on screen, step by step.
▶️ Watch Full VideoBecause most of those pop-ups are not coming from Windows at all - they are browser notifications from websites you allowed, or scam pages designed to look like antivirus warnings. A web page cannot scan your PC, and a real antivirus warning never asks you to call a phone number. Close the browser: if the pop-ups stop, remove unknown browser extensions, reset the browser settings, and clear notification permissions for sites you do not recognise.
You can run a second opinion as an on-demand scan, but never install a second real-time antivirus alongside Quick Heal. Two resident engines scan the same files at the same time, conflict, slow the PC and can make symptoms worse. Use a reputable scanner from its official site, run the scan, read the result, and decline or remove any real-time component it offers. One resident antivirus plus occasional guest scans is the correct pattern.
When two reputable scanners say clean but system-level behaviour is still wrong - settings reverting, unknown accounts, security tools being disabled - or when scans agree that Windows system files are damaged beyond repair. At that point the PC cannot be proven clean, and an unprovable PC should not be trusted with banking or work. Back up documents and media only, reinstall Windows cleanly, install Quick Heal from the official site first, and scan your data as you restore it.