After I opened a program, Avast showed up a pop up message and it seemed like Win32:Malware-gen detected. After that, there was an another pop up message. Here’s the message: http://s29.postimg.org/4ua3a5rzb/avast2014_bootscan11.jpg
Should I perform boot-time scan?
Yes, its a boot-time-scan which will scan the computer before the OS is even started.
Some malware can only be found this way as its hiding from tools when Windows running.
So its improving removal of stubborn infections.
If you need malware assistance follow this guide and open a new topic in viruses and worms section: https://forum.avast.com/index.php?topic=53253.0