So my dad recently got a new computer, but he says that the tower is to big for him. So I tried to switch the hard drive into the older computer, which has a smaller case. The older computer said the was no boot drive found. So I made sure the cables were plugged in correctly. Then is said it was recommended to boot is safe mode. It said there was an error with the start up and needed to repair it, which I did. Every time I did it said the repair was unsuccessful and it restarted. When I tried to boot normally it got the screen where it says windows is loading, then a blue screen would flash and it would go to the screen where it gives you the option to access the settings and then would load to the screen recommending that I load in safe mode. So I put the drive into the newer computer case and it worked. Anyone got any ideas why it is not working. Both computers had windows vista on their hard drives, but the older one uses an AMD CPU where the newer one uses a Intel CPU.