how to restore dell dimension 3000 to factory settings

First, if the computer has the restore partition, you should see a blue bar at the top of the screen immediately following completion of POST.  After two seconds you should see a message about loading the descriptor for PBR2.  If you don't see these things after you start or restart the computer, the restore function is not operational.  If you do see them you need to restart the computer, press CTRL and F11 toward the end of POST, and release both keys simultaneously before you see the message about the descriptor for PBR2.  If you are successful you will get a screen that has an option to restore the computer to factory configuration.

If you don't see the blue bar, try using Disk Management to see how many partitions you can find.  If the partition exists, you should find three.  First, a utility partition formatted in FAT-16 about 32 MB in size.  Second should be the NTFS partition used for the C drive; this one will be the largest partition on the drive.  Third should be a FAT-32 partition of two to three Gigabytes in size.  This last is the restore partition.  If you wish you can try to fix it, but you will need to study Dan Goodell's page found here:  Inside the Dell PC Restore Partition.

If you don't have the restore partition and can't fix it, the only thing you can do is find the CDs that should have been shipped with the computer and restore the system manually.  If you don't have the Dell Windows Reinstallation CD, you can ask for one here:  Dell Replacement Disks.  If you don't live in the U.S. you will need to contact Dell Tech Support for your region and request the CDs.