How can I remove a virus?

Your best bet is probably the Kaspersky Rescue Disk https://support.kaspersky.co.uk/viruses/...

If a virus is already on your computer, if it tries hard enough it can always hide from any antivirus you subsequently run. But Kaspersky Rescure boots you computer into an independent virus-free operating system with anything bad on your disk lying dormant and so should be able to root out anything bad it finds unhindered by its protestations.

If that doesn't work, are you sure you really have a virus? Or is the computer just running slowly or unreliably? The only sure-fire method is the nuclear option - backup all your data, grab all your licence keys using the Magical Jellybean Keyfinder (Google for it), then reinstall.

Once you're clean, install a free antivirus. If you were previously relying on Microsoft Essentials, try Sophos Home, which is also free.