It may be that there is a bad chip on the back of the hard drive.
Or it may mean a cable has come loose, or a BIOS conflict.
Usually it is a failed drive.
If you feel comfortable putting your hands inside the case... removing the two screws and sliding off the protective cover, you can remove and reseat all the plugs.
The Dimension 3000 is a computer that uses EIDE flat cables, and the hard drives are not expensive at some sources such as
www.zipzoomfly.com,
www.directron.com, and
www.tigerdirect.com among many others. You can replace the drive fairly easily if you have a #1 or #2 phillips screwdriver
At ZipZoomFly, I recommend Seagate drives because of their five year warranty. A replacement 80 GB is $50, 160 GB is $62, and 250 GB with a 1`6 mb Buffer is my choice at $72... all with free shipping.
You do not have to buy from Dell, but you do need the disc recovery set. The Windows XP disk is usually Maroon, Grey, or yellowish green for that model. When you cold boot to that disc, it will format the drive, then install windows.
Recovery the data from your other drive is possible in about 67 percent of the cases... you need to install it jumpered as slave, and the new drive jumpered as master, and see if the computer will see it. Otherwise, you need to have a technician's involvement. That might be more expensive than the drive is worth.