Need help with my Spyware

I have this horrid problem with a trojan and AVG free edition..
I have used Spybot and AdAware and e-wido and clean up and ccleaner, phew!!! and i regulary update and use these tools anyway..
but still
when i turn on my computer the AVG Resident Shield pops up and says "virus detected!"
When I click "Heal" and "Move to vault" it says it is successful but the Resident Shield window pops up again with the same virus/infection name.
It says
"While opening file: C:\WINDOWS\system32\orans.sys
Trojan horse Agent.CX"
please help please
thanks

Have try another antivirus ??
Since when i used AVG before .. i experience that too ...

You might have a rootkit, anti virus software can't always remove those.

Check it with GMER:
http://www.gmer.net/

Try to delete the file using this: http://www.bleepingcomputer.com/files/killbox.php

I have not tried my using it my self, but it is worth a shot