If you still suspect if there could be virus on that computer, Try to use a process explorer tool and check for suspicious process on your computer.
If you are an advance user you may also use Filemon(file monitor),regmon(registry monitor) to find a possible threat!
All of the above mentioned tools and utilities are from Sysinternals(Microsoft) and can be downloaded separately or in a bundle from the web site link below.
http://technet.microsoft.com/en-us/sysinternals/bb842062.aspx
-->Trouble running or exploring the tools, i would recommend you calling the Tech support guyz They would assist you removing the threats!!
Its more challenging and needs a lot of patience removing any virus by ourself!