It said that an AV program is already running so I could not turn it on.
E: Here's the reason why.
Windows Defender for Windows 8 & 10 is a full Antivirus and by default Windows shuts down Defender as the two will conflict and cause problems.
Prior to Windows 8, going back in time to Windows 7 etc. Defender was not a full Antivirus and was not turned off by default.
Avast can be run with Malwarebytes as the latter is not an Antivirus
I have been running these two in all my computers for years and I just installed both of them in my 18" Tablet as they come as android apps as well.
Get the Premium version of malwarebytes and here's why.
Say you get a spyware, the premium version will destroy it before it enters your computer as it is an active scanner but if you only scan once a week using the free version spyware would have already stolen all your data or a ransomware would have already locked all your files. In my opinion the free version of malwarebytes closes the gate after the horse escaped.
However the free Avast has everything you need. It scans email as well.
One really handy feature is Avast has a special Banking browser which can be used for entering passwords into sites or any online transactions etc. Basically it isolates itself from the rest of the computer so if you had a spyware/keylogger in your computer it could not capture your passwords etc. I use it for all banking and ordering stuff.
So if you have Windows 8 or 10 then use Defender as your antivirus but for Windows 7 and below it is not a full Antivirus
Defender and Avast are not compatible. Defender and Malwarebytes is compatible. Avast and Malwarebytes is also compatible. The full version of Malwarebytes is an excellent replacement for an Antivirus but costs money.
Why would you want to run more than one antivirus program on your computer. Generally it will create conflicts and most likely will slow down your computer. Two antivirus programs does not make you any safer. Avast is much better than Windows Defender. There are several really good FREE antivirus programs that you can get on download.com Hope this helps.
If you have Avast then you don't need Windows Defender.
Malware bytes works fine with avast the reason it's not working is your malwarbytes came from a look alike site that slipped you a Trojan.
Now first uninstall it and restart now go into avast and run the boot time scan set it to delete anything it finds.
After your run it.go into control panel folder options and click show hidden folders click apply.
Then go into c drive program files and both program data folders and delete the malware bytes folders.
Go back to control panel and hide those files again!
Now go to malware bytes .org and download malware bytes install it and it will now run good luck