backdoor.tdss.565/4005 avast only block to start,but reach infected hdd bootsector.Only DrWebcureit disinfect hdd bootsector.If bootsector infected (conhost) trying start every service
svchost/explorer and all going slow.Fix this shit,dont blame my language im finnish.
There are several tools that will clear this, but as of yet I do not know of any antivirus that can block this from installing, but Avast is one of the few that will stop it sending data.
Did you try a boot scan with Avast ? Did you try TDSSKiller ? Did you try aswMBR ? All of these methods will have a high degree of success