Im not too sure on the symptoms your computer is facing. In what way has it hijacked your computer, and what is the nature of it? Can you access your system setting and files, or does it only just effect the internet?
Here are your options (loose due to the fact I don't know what you mean by hijacked)
First, you should backup all your data if you can, on a CD or external HDD. Make sure you search every folder important data may be. take a list of all the programs and/or games you have. Backup any saved games you have by saving the folder of the game in your program files section.
Once you have backed up, you can try and system restore your computer to an earlier date. That will be under Start>accessories>system tools>system restore.
Try restoring your computer to an earlier date, before this issue occurred.
However if that does not work, you can try attaining a copy of an anti virus software, and scan your computer.
If that fails then you might have to take you PC into a shop and they will have to format your HDD and reinstall windows.
There are other numerous ways to help remove malware, however you must be an expierienced user,
afantispy.com has hijacked my computer, how can I get it off without paying the $49.95 fee?