If you're sceptical of the machine over TeamViewer, create a virtual machine, install TeamViewer and remote access his computer from that. But that is pure overkill in my opinion.
Run a bootable antivirus, such as Kaspersky Rescue Disk 18 and/or ESET SysRescue. You could burn these to disc as well as a Windows 10 installation disc and another disc containing tools such as ComboFix, AdwCleaner, etc and pop the discs in the post. Advise your father not to turn the machine on until he has ran the rescue discs first.
After the machine has had a preliminary scan for infections, start the machine up in safe mode with networking and get to work on TeamViewer, starting with the tools on the provided disc. Then use an online virus scanner, such as ESET Online Scanner, to scan all his drives for infections.
From then on, work towards creating a backup with a mind to completely reinstall Windows.
If you want some other suggestions for Malware/virus scanners to pop on your disc, these are some that I recommend:
Run a bootable antivirus, such as Kaspersky Rescue Disk 18 and/or ESET SysRescue. You could burn these to disc as well as a Windows 10 installation disc and another disc containing tools such as ComboFix, AdwCleaner, etc and pop the discs in the post. Advise your father not to turn the machine on until he has ran the rescue discs first.
After the machine has had a preliminary scan for infections, start the machine up in safe mode with networking and get to work on TeamViewer, starting with the tools on the provided disc. Then use an online virus scanner, such as ESET Online Scanner, to scan all his drives for infections.
From then on, work towards creating a backup with a mind to completely reinstall Windows.
If you want some other suggestions for Malware/virus scanners to pop on your disc, these are some that I recommend:
- Emsisoft Emergency Kit: https://www.emsisoft.com/en/software/eek/
- AdwCleaner: https://www.malwarebytes.com/adwcleaner/
- ComboFix: https://www.bleepingcomputer.com/download/combofix/
- HitmanPro: https://www.hitmanpro.com/en-us/hmp.aspx
- FixExec (might help with programs not launching): https://www.bleepingcomputer.com/download/fixexec/