Dell Dimension 8100. No start!

The exact beep code for that machine means that you are using unsupported RAM.

This Dell computer uses RAMBUS memory (aka RDRAM / RIMM)... not DDR or DDR2 /DIMM

Try this:
Use only one memory module (the oldest one if you added any).
It will work with no problems.
ok, replace that module with the largest capacity (1GB??) or with the newest module. May not work consistently...
Check with Dell website to determine what brand RAM is supported on that machine.
or purchase RAM directly from Dell.

ok i know this 80 % either you have no ram in the system or the ram is faulty and or not placed correctly

Look on the back of the case where the devices plug into it. There will be a set of 4 led lights. starting from the top down oe left to right depending on how they are situated, look at the lights and this is a doagostic of what is happening during the boot sequence. These are green and yellow lights and their order and color are the signifigance of what is wrong, if you have your manual, the meaning of the colors is in there under troubleshooting. I'll see if I can find it......check this out

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

Disconnect all devices from the power supply EXCEPT the motherboard
Remove any extra cards including video etc.(plug monitor into the onboard)

If you hear any beeps these can indictate where the fault is.
either of these sites below will help you further with that

Beep codes Pc

More beep codes

Power up the pc and see if the fans are working.
If not then double check the power connections to the board.

If you still have no fans it is time to suspect the power supply as the probable cause.

If the fans worked then you should have gotten a display which told you there was an error and offering you a chance to go into the BIOS. ignore it and shut down the PC.

Now connect one drive only and boot again.

Repeat that until you identify the component that is giving you a problem.

Once you find the problem then remove or disconnect and carry on with the rest to see if another component might also cause a problem

If there is only one problem device then you may want to investigate that device further, Unless you don't mind replacing it

You probably need a new motherboard as this can mean that your CPU is fried or just the motherboard is shot (5 beeps). I would try removing the RAM from the motherboard and re-seating it.