Yesterday I scan my pc and Avast detected that a file ( a virtual machine ) was a trojan but is a false positive and I have my work of a month on that machine. I couldn´t see the file in the chest I think because is a biggest file (more than 11 GB) and I could find the way to recover it. Please Help me. I really need to restore it.
When avast! displayed the warning - did you select to Move it to Chest, or Delete?
No Avast didn´t give me the option 
Did you set avast! to silent mode?
No I went trought the console, I select all folders on my computer and start scan
avast Home version doesn’t take action autonomously it scans and when it detects an infected file it alerts the user and stops the scan until the user chooses what action to take. It will then carry out that action and move on with the scan until it finds another or the scan ends.
So what version of avast have you got ?
Given the size of the file and as you say that avast couldn’t send it to the chest (you did select an action) that would fail, so in theory it should still be in the same location as avast wouldn’t just delete it because it couldn’t move it to the chest.
Silent Mode is only available in the on-access scan not the on-demand scan that the Flor Velázquez did.