How to complete remediation

Remediation Incomplete.

I got a notification from Windows Defender that a Trojan had been detected on my laptop, but “Remediation was Incomplete” and the threat remained “Severe”. How do I complete remediation please?

So far I have tried: 1. A Windows Defender Quick Scan – nothing detected; 2. A WD Full Scan – nothing detected; 3. A WD Offline Scan – nothing detected, and 4. a Malwarebytes scan – nothing detected. So I scanned with Microsoft Security Scanner (MSERT) which froze at the three quarter mark having identified 75 infections. I then freed up space by deleting Firefox cache files and scanned again with MSERT on two occasions several days apart, with the same result -the scan froze each time at the three quarter mark and wouldn’t complete.

NOTE : I am running Windows 10, 64 bit. The malware is “ Trojan HTML: Phiz!pz”. The MERST scan stopped twice on the same file (C/Programme files (x86)HP/HP RegistrationService/HPGenOOBE,exe) and once on (Ereload\install31.swm). Defender said the affected items are Firefox\Profiles\f590f2zl.default\czche2\entries. Windows routine Back-Up is obviously affected too since on the last two occasions it has tried to run it has been stopped by the Trojan.

NOTE 2: There is plenty of space on the C: G: and D: drives and 1.41 GB remaining on the E: drive. Around 30 million files had been scanned by the time MERST froze and around 80 infections had supposedly been detected

Thanks for any help.