Help! Norton 360 is detecting a virus called 'trojan.ADH.2' but keeps saying removal failed

Hello,

 

Can somepme please help. My Norton 360 is detecting this trojan, but keeps coming up with 'removal failed' and when I try to delete the file manually it tells me I don't have administrative permissions to do so, despite me being the only user on this computer. It's been detected in a file called 'systemk.dll' which I believe is a windows system file. I've tried using the norton power eraser but evey time I try to start that I get an error message. I really have no idea what to do. Also when I do a full system scan norton doesn't detect it anymore in the security risks detected part of the scan, yet a norton window randomly pops up saying that there's a risk and this virus is listed. The risk is also listed as being high

Please please help