Do you know anything about the virus?
Do you know what the process name it uses when its running?
If so you can go into safe mode and use file search to find it and delete it.
If you dont know the process name.. you can go to
Start -> Run -> msconfig -> Startup
look for anything thats checked and you dont recognize and google it.. find out what it is..
It will likely be on this list (altho there are other start up methods it could be using). Simply unchecking it wont work because if the virus is currently running it will instantly readd itself to the startup list.
Once you find out the process name you can find that mfer in safe mode and delete it