Al, I would check the SATA cable from the motherboard to the hard drive first. They're a bitch for coming loose at either end unless they have some form of locking clip on them (some cables have them, some dont)
Eh? Just seen your latest post Al. You appear to have been fobbed off with a somewhat older computer than you probably expected there matey. I dont think Dell have pushed anything out with a P4 cpu for at least a couple of years. Was it sold to you as new?