That definitely sounds like a hardware issue to me. Do you have a warranty still in effect with Dell?
I've had a Dell Dimension for a while now, and it's always worked great. Very recently, however, whenever I start up, I get a prompt screen early in the load up process that says the primary drive cannot be found.
It then says something like "Hit F1 to continue" and when I do, the machine loads up XP just fine.
I only have one hard drive, I checked all the drive cable connections, I have added or changed any components or related settings - everything seems to be in order.
I'm guessing that since it's so early in start up process that it must be a straight up hardware problem?