What kind of port did you plug the 4 pin connector in to? Was it on the motherboard, hard drive, graphics card, disc drive...? If it did damage to your motherboard, you should be able to still extract the data off of your hard drive by removing the hard drive and inserting it into another PC. You can test to see if the PC still boots by downloading and burning the Ubuntu (or any other Live CD Linux distro). You can get Ubuntu at www.ubuntu.com
and then burn the .iso to a blank CD. Put it in the drive before you boot the PC, and when you do it should boot into the Ubuntu operating system. If not, go into BIOS and change the order of the devices boot.