have any options changed in the BIOS as to the sata mode?
You could try run a linux live cd (ubuntu 9.04 should work fine) just to rule out the possibility that its a OS configuration problem.
nothing changed in bios, that I know of as the bios has a password from the previous owner and I can't get access to the settings. So obviously no one has modified them, but that's not to say something else, installation of programs has created an issue. Not sure when the problem started, but when I tried to burn a DVD I found both units were not being recognized.