Did the system boot properly before? Is the HDD the only device connected to the IDE cable or is there another HDD or optical drive attached to it?
If the only device, it could be a defective cable or the HDD itself. If not the only device on the ribbon cable, verify that both are not set to master or slave. You can set them both the CS (Dell default config).
If you can change cables, try that. Also, verify that your BIOS detects the HDD and has it selected as the default boot device.
I have just one HDD and the BIOS does recognize however, it refuses to boot it up. Does Dell make their systems incompatible with other brands ??
Dell doesn't make the HDDs incompatible, rather Windows installs specific drivers/files for each system based on the hardware present at install. Switching from one PC to another can be done, but it is better to just reload the OS on the new platform. Makes for a better, more stable install.