backdoor.trojan globalroot\systemroot\system32\gsvxcbn(a whole bucnh of other letters).dll

Hi,

 

Norton antivirus scanned my computer and found a backdoor.trojan which cannot be cleaned/quarantined/deleted. It says the file is globalroot\systemroot\system32\gsvxcbn(a whole bucnh of other letters).dll . Does anyone know how I can remove this??? Please help!!!

 

I'm a newbie by the way, so will need step by step assistance!