Hi Joe, i have a specialisation in these and other pc's from pc world. All of them have the same problem.The plug you describe powers then processor. However this plug is a required item to power the cpu, doubtless you will have power to the board (unless then power supply has also blown) the cd and hdd will be heard to operate and the cpu cooling fan willbe running. This means the motherboard has blown. I supply board to replace these, better quality, longer life and full instructions to change it over and a disk to restore you version of XP. contact me on compdoctor2005@btinternet.com or by phone at 07926-106150
Chris, October 2008