What do I do if, after formatting my hard drive, my computer doesn't recognize my hard drive?

I had a similar problem. If you are trying to install XP, you need to include the SATA drivers on the installation CD for XP. You know the part where you get the blue screen, and at the bottom of it it says what it's installing, drivers, RAID, etc.? It's at that point when it installs the SATA drivers and THEN only after that you'll be able to see the hard drive to install to. You'll need to create an ISO image of XP and include the SATA drivers. PowerISO works great. That's what I had to do.