Why are some so quick to defer issues to viri and other malware when they encounter the abnormal? My personal rule is, if you place safe on the Internet, then the possibility of such issues being viri-related should only pop up when you've exchausted all your troubleshooting ideas. What happened to troubleshooting first before determining a possible cause?
Anyway, as Skepticals said, the task manager can be disabled by group policy or local computer policy...I think the Run command can also be disabled. Try going to C:\windows\system32\ and running lusrmgr.msc (Local User Manager). Look in the Administrators group to determine if you are actually an admin on the computer. Even if you are an admin, you may have group policy applied to your account or computer, so you would have to check (like Microsoft loves to say) with your network administrator.
