Ok, disconnect all peripherals except those needed to boot up (mouse and keyboard). Disconnect all memory, clean the contacts on the memory (new pencil eraser good for that, then seat the memory back in the machine. (Please don't forget the static strap). Try it now. Kernel panics happen for many reasons but on start up they occur for usually three reasons. Faulty peripheral hardware, faulty RAM, or a corrupted boot file. If you fix it with the advise above then you know you have a bad peripheral or one of your RAM sticks is bad. If not, oh well, time to reinstall OS-X.