If Task manager stays open for a few seconds and disappears, then some remnant of the virus is still there. There are different viruses which do similar things, does your friend know which virus it was?
Which version of Windows is it?
Can your friend run msconfig and regedit?
Get your friend to update his virus definitions. Boot into Safe Mode and run the scan again (scanning all files).
If the antivirus makes no difference, you'll have to do it manually.
You have to enable Explorer to show all files first. In My Computer or Explorer, click Tools, Folder Options, View tab, (1) Tick show all hidden files and folders (2) Untick "Hide file extensions for known file types". Click OK.
Go to the C:\WINDOWS\system32 folder, find a copy of taskmgr.exe, make a copy, and rename the copy to taskmgr.com
Do the same with msconfig.exe and regedit.exe.
Double click taskmgr.com to see if it will stay open. Try to find any process running which might be the virus. Note down the name of the file that is running.
Double click msconfig.com, look under the Startup tab, and see what's there. If you see a Winsock 2 driver, note down the path on the right. It may not be winsock 2 but something else. It's probably a Run Once entry in the registry.
Post back if the new virus scan doesn't make any difference.