Sony vaio laptop returning virus

Question

Hi
I have a Sony Vaio laptop which keeps getting a trojan everytime you reconnect to the internet after deleting the offending item with the antivirus.
I have tried several different Antiviruses, Anti-spyware which always remove it fine but keeps coming back.
I have tried disabling system restore, again with no effect.
The antiviruses seem to think origin is in Windows 32 sustem.
Look forward to hearing from anyone who can help
Thanks