Windows defender offline scan shutdown before scan complets. Virus?

I got a big problem. My windows defender offline scan keeps shutting down before it reaches 100%. I am Norwegian but will write in English. 

Problem

My windows defender keeps shutting down before the offline scan can complete. It usually stops around 92%, and this is on multiple computers across two different networks. 

Suspiosion

I have a strong feeling it is a virus that has changed the settings on windows defender. My reason to believe this is based on a number of observations and pictures I've gathered from an infected computer. Since early February this year, strange things had been downloaded into my system 32 and alot of new prossesors and tasks have appeared in my taskmanager. Along with 31.000 changes in my security log on the eventlogger. 

Troubleshooting

First I tried to delete these new files that were constantly being downloaded, but then all a sudden there were made, undeleteble by 'trusted installer'. Then I tried downloading and running different rootkit and bootsector virus scans. Many said the computer was healthy, others canceled out just like the windows defender offline scan. Then I formated the C drive (only drive on the system) and reinstalled windows 10 64bits. The same problem was still there. Then I even flashed the bios. Nothing is working..

I need some professional help on this as I am too afraid of using the pc. 'Bitlocker decryption devise' was also installed and I can't afford to be lock out of my pc..

Is this a part of any new windows update or is this an actual threat?

You may answer in Norwegian or English. Both is acceptable depending on what works best.

Mvh

Marcus 🙂