Ok , I have also tried to swap out my HDD on my computer with my other HDD from another computer. They are both IDE/ATA harddrives (PATA) They both use 4pin molex connectors to power them 12 volts , GND , GND , 5volts ANd they both use 40pin ribbon connector for data transfering. One harddrive has windows 2000 on it the other harddrive has windows xp. I believe but are not 100% sure they both use a file system format NTFS. My question is when I switch out one of my harddrives into the other computer I get this blue screen saying Inaccessible boot device" blue screen check if the cables are installed correctly and reboot ,...etc etc I know the cables and hardware is installed correctly.... so I don't understand what is going wrong? I looked in the Bios but I didn't come across any setting that would effect the HDD from booting.... The only thing I am looking at is maybe the jumper they all are set to cable select (which most of all my harddrives are set to even the one that was working in this machine before I switched it out) I don't really thing moving it to master would be any benifit if their is just one HDD in the machine to begin with. Both machines are around 2003/2004 I think where it is crashing and giving me the blue screen is right when you see the windows screen (so it is crashing at a bootloader or something) That means the bios actually handed control off to the master boot record code that it thru into memory..... Also one of my bios is old so could this be a barrier problem or LBA/CHS problem.....? I am take a harddrive that was in my older computer/older bios and putting it in my newer computer.... the HDD is 40GB and my bios has it listed correctly as that the original HDD in my newer computer was 75 GB and the bios had no barrier with this.... so I really don't think it is that. I know that both the HDD's are good because they work in the computers they came with and still do if I put them back.... so it is not a defective sector or HDD I also know that the chipsets are almost exactly the same What the *** less could it be and how do I fix it??????????????????????????????