the old (hitachi - hdd was with an Acer aspire tho still unsure of bios or where to look for that !,it was with this intel celeron cpu 550@2.00Ghz 2.00Ghz memory 1Gb system type:32 -bit operating system vista service pack 2 this all failed in an asytypical fashion the hard drive loaded but everything would fail or just slow itself to a blunt repetitve stop.,so on replacing it with samsung i need to know why i cant change the operating windows from vista to xp with a setup disc i iso . replacing the hdd is fine and the setup works but after a few minutes of loading files it sais it cant find hard drive at all . though, i know when i enter setup it sais 500gb hard drive !HeLp pls