I installed windows from a pendrive that my friend gave it to me, thinking it was original one I installed it. I never knew about checksums before installing the os from pendrive. But then realising it might contain a rootkit or other malware because my friend don't know much about computers. I then downloaded an official iso, formatted all the partitions and deleted them and installed it. After installation I installed bitdefender and malwarebytes anti-malware. Did a full system scan twice ( scan for rootkit ticked on) both of them found nothing. Then I downloaded other software from bleeping computer and did a scan with tds killer, combofix, adware cleaner, aswMBR, hitmanpro,JRT they found nothing. But after that I switched off my bitdefender and ran a GMER scan but when I clicked on scan it showed many error messages. So I restarted pc and clicked scan button but same thing happened again. Then suddenly malware bytes Real-time protection gets turned off I switched it on but as soon as I click on button it turns back off. After pressing ok to those errors it goes for a scan but scan stops withing few seconds or in a minute.