Wierd Problem

Hey, I have a wierd problem with my PC. Few days ago my PC:s hard drive broke ( 160GB, sata 1 hdd), so I bought a new one WD 1,5TB Caviar Green. My PC is so old that i had to set the sata 2 hdd to sata 1 mode ( slower ). First when I booted it found the WD hdd from the bios, then I tried to install Win XP.. And when im there it says "there is no drives" then I was like wtf. ( I have also tried install win 7, same thing) I booted the PC again, back to bios, and it didnt recgonize it? I booted again, same thing... Only if i take the power cable off and then put it back and boot, it finds it. But when I boot it again, this happens.. I dont get this... Please help... Thanks