Unplug the power cord, hold the power button in for 15 seconds, open the case and remove the cmos battery for 15 Minutes (note the polarity of the battery before removing)

 

Reinsert the battery in the correct polarity as removed.

 

Close the case and plug in , now try to boot.

 

http://support.dell.com/support/edocs/systems/dim2400/en/sm_en/rmvcvr.htm  open cover

 

http://support.dell.com/support/edocs/systems/dim2400/en/sm_en/battery.htm  replace battery

 

 

 

http://support.dell.com/support/edocs/systems/dim2400/en/sm_en/index.htm your 2400 manual

that didn't do anything.  i'm still stuck on the same screen.

 

 

1. Start disconnecting hardware from the motherboard (making note where things go back)

There may be a bad piece of hardware that is causing the Post process to hang, (cd rom, pci card, memory module, ect) and by unplugging it you may be able to get the Post to complete.

 

Unplugging things one at a time and trying to boot will reveal the hardware that is causing this.

If you have more than 1 memory module, remove one, then after trying to boot and no success, put it back in, and remove the other one, and so on.

 

 

http://support.dell.com/support/edocs/systems/dim2400/en/sm_en/index.htm  your manual