The Dell 3000 has been a reliable, basic, budget unit.
No bang is normal.
You may have blown a capacitor, motherboard, or power supply.
The capacitor will be a little barrel-shaped object resting on the motherboard. There may be many of them. Look for grey, brown, or rust colored powder. Look for any of these "barrels" which are swollen or which have distorted or rounded tops. A typical failed capacitor will have a split down one side with the powdered innards leaking out. There could be a film of dust throughout the computer.
A blown capacitor means you need a new motherboard. If you don't get a motherboard from Dell, your hard drive and Windows will not work. Expect to pay $100 to $150 to replace it from Dell. If you buy from eBay, you will need assurance that you have a Dell certified motherboard designed for that model that has the correct EEPROM installed, so that your Windows is dtecting the correct information about the board.
If you were running games, or photo editing, it may have overheated some components or damaged the motherboard, or burned out the power supply.
The first thing to do is check the power supply. That is the big metal box that has all the wires coming out of it.
The easiest way is to buy a power supply tester from a computer store,
www.geeks.com,
www.cyberguys.com,
www.newegg.com,
www.directron.com,
www.zipzoomfly.com,
www.outpost.com,
www.techdepot.com or other. They usually run about $11 to $15 but can be as high as $25 for the better ones. Test the power supply with the tester. Outside the computer.
If the power supply, something beyond your ability to fix has gone bad. Call a technician. It may not be worth fixing.
If the power supply is bad, replace it with one of the same size, but at 300 watts or better. Quality is important. See the lists on this formum about quality power supplies, but you do not need an expensive one... though you should expect to spend between $50 and $75. You will need to understand all the connectors and the differences between a 20 pin and a 24 pin power supply, and how to use them.
This is a very big job. It will be stressful, most likely, and will take a lot of time. But it is not rocket science, and most people with a brain and basic skills with tools can do it, by taking their time and thinking it through.
But it you do not feel up to the task, have someone look at it who is very experienced... not just the guy down the hall or the next door neighbor's kid.