Compaq Presario? Well there is your problem right there!
Check the IDE cables in the back, and then if they are connected properly, go BACK into BIOS and run an Auto IDE detect. If THAT doesn't work, try running the Detect Hardware wizard from the control panel and if it doesn't show up in the plug and play section, run a deep scan (which is usually meant for things that plug into the ISA slot and different jazz like that). I hope something in there helped!
BTW, was there something you did that made it stop working in the first place?
Jon