Hi there ninja,
This sounds to me like the computer has become infected by some kind of a virus or malware or something to that effect, it's a very common things nowadays with such easy access to the internet for most people and the kind of things floating around the internet are in many cases extremely well hidden and quite nasty if they find their way onto one of the devices that you own, even more so if that device can communicate with other devices through the means of the internet etc...
You'll basically need to at a minimum attempt to cleanse the computer of any malicious software that may be running on it through the means of virus scanning software or possibly by taking it to a computer repair store and asking them to do it for you at a considerable expense to you.
I hope this helps and good luck with getting it sorted out
