I see you posted this last night, along with another post asking about ransomware (Citadel/Reveton) your dad had a problem with. Is this a different computer, or a duplicate post with the same problem?
Please see: Remove the FBI Online Agent Ransomware (Uninstall Guide)
Note where it says:
'Please remember that this is a computer infection and that the FBI is not locking your computer, so please do not be worried about the messages in the lock screen. This infection is detected by a variety of anti-virus vendors using the Trojan:Win32/LockScreen'
'Symptoms that may be in a HijackThis Log: O4 - HKCU\..\Run: [dllexp] rundll32.exe "%AppData%\dllexp.dll",exp
There are various other ways of removing it, if the two methods prove unsuccessful. If this post is a separate issue than your dad's, kindly post back (with details included) and let us know.
Best of luck..
This trojan horse has embeded itself in
It says : Object is inaccessible
How can I fix this?
It says the computer/file is infected.