Services.exe trojan Help Please.

Hello,

I have a trojan attached to my Services.exe file that is unremovable, the trojanzeroaccess tool was unable to find or remove, and neither was the Norton Eraser program.  I do not have a copy of my Vista Disk, but from the initial menu I was able to perform a startup repair (nothing found), a system repair (2 sweeps, nothing found).  I can't seem to shake this bug. Any and all assistance would be greatly appreciated! I am running a Toshiba Laptop on 32 bit Vista with FireFox.

Thanks!

Jessie