trojan viruses..need help,would be greatful

[becks]

well i started my pc and a pop up came saying you have a trojan sumthing virus i cant remba the whole name and it said it cant b reparied so i went ok, this was a norton anti virus pop up, so afterr this i ran norton anti virus and nothing was found. so can sum 1 plz help me and tell me what i should do

 

[Jack Flash]

Get a Trojan Removal tool, such as Trojan Remover and run it.