Reformatting a computer help needed?

Hey guys, I am having a lot of trouble reformatting a computer. I used Darik's Boot and Nuke (Which took literally 56 hours!) to wipe it since it was ridden with viruses. I have an iso burned to a blank disc (windows xp) to start it back up but nothing is working. I keep getting "No boot sector on internal hard drive" error even though I am trying to start it from a disc. Could anyone please help? The computer is a XPS M140 Dell laptop and I have a USB if it needs to be used as well. I have been troubleshooting this for a few hours now. =(