Let's talk a little Windows maintenance...

After you've done something like a boot time scan with Avast, which works a lot like Emco's 'MoveOnBoot' in that it does its thing during a reboot, in between when the memory is unloaded and reloaded, so that it has access to all the files that are usually hidden or system files, and assuming that during that, it found some corrupted CAB or other files, and you'd like to refresh everything to restore the correct image of your system, you can run DISM.exe, which is the Deployment Image Servicing and Management tool. And you should run that with Admin privileges in Command Prompt, as shown below...

When it completes its little bar graph in 20% segments, it shows you this....

And then all you need to do is enter the word exit at the command prompt to get out of there. If you'd like to view the log file for it, look in:-
C:\Windows\Logs\DISM\dism.log  And I should add that this applies to Windows 8 only. The Windows 7 version does not recognize the option "/RestoreHealth".