I need some info before offering a lot of suggestions. Otherwise I might send you in the wrong direction.

Is this computer new to you or have you been using it and now have the problem?

I assume that you have checked all cables to make sure they are properly seated.

Can you get to the cmos by tapping the del or f1 key as it attempts to boot? If so change the first boot disk to floppy and boot to a:\ prompt. This will allow you to reinstall examine the c: drive to make sure that it is intact. Once you boot in dos you can reinstall windows or use the dell recovery disk to reestablish the operating system.

If you can't boot in dos, unplug all cables to your hard drive, then reboot. If the hard drive has failed this will often allow you to boot to dos via the a: drive.

Remember that the primary reasons any computer will not boot are the following:

Loose or bad cables.
Corrupted or defective hard drive.
Bad memory.
Bad power supply.
Bad processor.

It is fairly easy to test the first two. As you go down the list, it becomes more difficult because most people don't have extra memory, processor or power supply at hand.

If you are not in a hurry, and don't mind spending a few bucks, you can order from a StarTeck.com distributor a PCI Post Diagnostics Test Card (approx. $40). It is similar to performing a computer test on a car. You get a number error code on an LCD screen that indicates the reason for your problem. For $10 more you can get a Power Supply tester. Be sure to choose the Power Supply tester that is appropriate for your computer.

Another, somewhat drastic measure is to reset motherboard defaults. I recommend that this not be done until you have attempted everything else. UNPLUG POWER CABLE BEFORE PROCEEDING. On recently built motherboards this can be done by changing a pin setting on the board and then turning on the power. UNPLUG POWER CORD AGAIN. Return pin jumper to original setting and replace power cable and attempt to boot.

To find the jumper, identify the MB and do a Google search for the MB specifications.