Problem With Removing Trojan Horse

Hello,

I have Norton Security 2009 and the problem with it is that it has detected a Trojan Horse in my system but it doesn’t removes it, it only blocks it and every five minutes an information comes up that Norton has detected a Trojan horse and it has been blocked, but when I run a full scan system it doesn’t finds anything. 
Also every time the Trojan Horse place is changing one time is C:\WINDOWS\Temp\tqbd.tmp\svchost.exe and when the information comes up again it changes it’s location but the beginning is always the same C:\WINDOWS\Temp.

Can somebody please tell me what should I do to remove this Trojan Horse completely?