OK, here's the deal. I have a Compaq/HP NC 8430 that I needed to install a new Hard drive. I bought a 500 gig sata HD and installed it. It passed the HD diagnostics with flying colors. When I tried to install the OS (XP pro) it went thru all the preliminary files but when it started setup it told me there was no HD found. after researching that model I found out that it won't support a 500 gig HD so I returned it and bought a 80 gig sata HD. Thinking my problem was solved. But it wasn't, I got the exact same results. I then installed the HD in another machine and loaded the OS with no problem but when I put it back in the NC8430 it would not recognize the HD but the BIOS see's it and it passes the BIOS HD diagnostics....HELP!!!!