Hello hurling and welcome to Seven Forums.
I think I'd start by running Windows Defender Offline to check for malware. This is a bootable disk and needs to be created on a machine that isn't infected. Also, the machine used to create the WDO disk must be the same architecture as the infected machine (if your father's computer is running a 64-bit version of Windows 7 then the other machine must also be running 64-bit. Windows Defender Offline
If this returns the computer to an operating status scan with additional free on-demand scanners below. If the machine doesn't return to operating stuatus, see if you can access Safe Mode with Networking through the Advanced Boot Options menu. Advanced Boot Options
If you can, run some free
on-demand scanners such as these: Malwarebytes ESET Online Scanner
(website was down for routine maintenance but should be up soon) HitmanPro SuperAntispyware
You could also try to use System Restore and roll back the computer to an earlier date/time. System Restore