Verify that your motherboard does recognize the 160gb as a 160 and not as smaller (138). Alot of motheroards have this limitation in the bios. If it does not recognize it correctly, go to the motherboard manufacturer's website and see if there is a bios update to fix the problem or you could disable the onboard controller and get a controller card.
I had to update my webserver's motherboard bios to accept the (2) 160's I am using in it now.
HTH