I have a Dell B110 with upgraded EVGA Nvidia Geforce 6200, Creative Soundblaster Live 24-bit, Linksys Wireless-G Adapter with Speedbooster and an added Seagate Hard Drive as slave.
I recently disconnected the slave hard drive of my PC and switched it with a compatible ATA hard drive (with the jumper set to cable select and the slave connector of the ribbon cable attached) from my friend's dead computer to recover the files.
I was unable to boot at this point so I removed this added hard drive, put it into a different PC and was able to access the added drive fine.
When I put my original drive back as the slave, it would no longer boot, but instead showed a flashing amber light instead of green in the power light. I went through the Dell Support Wizard which involved removing all peripherals, power+data cables from drives, RAM, expansion cards, and reseating the two motherboard power connectors. Doing this process changed it from flashing amber to solid amber. According to Dell's support site:
I am unsure what is causing the problem or what I should do at this point.