Doug recently replaced a power supply, and now the computer won't boot up to his main hard drive. Leo says that the SATA cables may have been swapped and that can confuse the BIOS. He should disconnect the data drive and see if it boots to the boot drive. If it doesn't, he can swap out the cables. He should also clear the configuration data in the BIOS so that it can reset. There's also a possibility that his boot drive is damaged, so he should check that. Getting rid of the master boot record on his data drive will prevent confusion as well.