My dell dimension 8100 has an intermittent fault

According to Dell's list of light codes (available here), this means "memory failed to be sized or enabled". In other words, it's a memory issue. Dell suggests reseating the memory modules. I would recommend removing the modules, make sure the contacts are clean (use a pencil eraser to gently clean them if they aren't), and use compressed air (available in cans at office supply places) to blow any dust and dirt from the module connectors on the system board. Then reseat the modules, making sure they latch properly into place.

If the problem continues, you might have a bad module. Sometimes they act up intermittently. Or it could be a symptom of a developing motherboard problem. Try cleaning and reseating the memory first as that's pretty common.

http://support.dell.com/support/edocs/systems/dsleest/codemess.htm#diagnostic_codes

here are the codes-decoded above...
check your monitor cables and wires, make sure everything is connect. If that doesn't help, test the monitor with another computer, if that doesn't help, look to the video card. Reseat the vid card and reboot. If that fails replace the video card.
Hope this helps. please leave rating...thank you