I had a Dell 960 and had the same problem initially. All SATA on this machine, no ATA.
i had to make sure the BIOS had RAID disabled entirely, and then I had to install onto an external USB drive first. When I booted from that drive after instal, I could see the internal drive, and then I installed on that one and could boot from it from then on, so I kinda had to do two installs to get it to work, now I boot from the internal fine.
Not sure if this is something up with Dell's but I have seen a few other people with the same issue.