Dell™ Dimension™ 2400 Series
This model is not a workstation.
It's possibly but extremely unlikely a shorted drive or shorted data cable wiring could cause your problem - you could try disconnecting all of those, then boot and look in the bios Settup.
(The following also applies to floppy data cables)
It is common to un-intentionally damage IDE data cables, especially while removing them - the 80 wire ones are more likely to be damaged. What usually happens is the cable is ripped at either edge and the wires there are either damaged or severed, often right at a connector or under it's cable clamp there, where it's hard to see - if a wire is severed but it's ends are touching, the connection is intermittent, rather than being reliable.
Another common thing is for the data cable to be separated from the connector contacts a bit after you have removed a cable - there should be no gap between the data cable and the connector - if there is press the cable against the connector to eliminate the gap.
80 wire data cables are also easily damaged at either edge if the cable is sharply creased at a fold in the cable.
Try another data cable if in doubt.
If removing the cmos battery and then installing it again with the power cord disconnected does not restore the bios to default settings that enable both IDE controllers, then probably the bios is damaged, or the mboard is damaged, or both.
In that case, you could try flashing the bios, but make sure you use an appropriate bios update, follow the flashing instructions, use the bootable Dos floppy method to flash if available, and load bios defaults in the bios after the flash has finished, after you reboot the computer.
If you have only two drives, the 845GV main chipset on this model's mboard is new enough that it doesn't matter whether a hard drive and an optical drive are connected to the same IDE data cable - both will run at their full speeds.