How can you remove Trojan MusicSearch.AM in a subdirectory under c system volume?

Assuming you mean a subdirectory under 'C:\System Volume Information' and your anti-virus application has detected but cannot fix the problem :- select System Restore tab in System Properties (WinKey+Pause) and check the box marked 'Turn off System Restore on all drives', confirm, close System Properties and reboot. This will clear all files in 'C:\System Volume Information' and therefore the MusicSearch.AM problem. 'C:\System Volume Information' is not just a hidden folder, it's also system protected and as such, anti-virus software cannot write to any file within and therefore cannot delete or quarantine any infected file detected. To turn on System Restore, just reverse the above procedure. Hope this helps, Canis.