Tell us the full name of this "keygen" that opens every time the laptop is started. What does the splash screen say?
Can you take a screen print, and upload it to an image hosting site like ImageShack or PhotoBucket, and let us have a link to the image?
What does your son say this 'keygen' is supposed to do?
What you deleted from the Prefetch folder is just a type of shortcut to the actual software, (if it is software), and not to the software itself.
In case it is malware, I would update your anti-virus and anti-spyware utilities and run a full scan. Also, I would recommend you download the free anti-malware utility Malwarebytes Antimalware, install it, update it, and run a full scan.
Just to be sure we understand what you say, do you mean the Startup folder in the Start menu > All programs? Also, did you check the Startup tab in MSCONFIG for any entries that may refer to this keygen?
You need to know that torrent files are file sharing files, (known as P2P or Peer to Peer). These are all too often used to download and share copyrighted and pirated files like software, music and videos, and that is illegal in many countries. Also, many of those downloaded files can be virus infected. How did your son download this file? Is he using specialized software he has installed on this computer? What files is 'he' sharing with others from this computer? Your private document files?
My son downloaded something called a keygen(?) that starts every time I start up my laptop. It puts a splash screen in the middle of my screen at startup and leaves it there until I close it. He downloaded something called a torent file which sounds like something he shouldn't be doing. I think I have uninstalled the associated file. When I do a file search for keygen.exe, the file is found in the C:\Window\Prefetch subdirectory. I have deleted the keygen.exe file from the Prefetch directory, but when I startup the next time, the keygen.exe file is there again. Somehow it regenerates itself.
I checked the Startup subdirectory, but there isn't anything there that would start the keygen.exe program. I also ran the msconfig program to see if there is something there to start this program, but there wasn't.
Where else do I need to look to get rid of this program?
I appreciate your assistance.