I saw that there are other questions like mine here. But O also saw that some problems where solved with fixmbr from a Windows 7 recovery console, but that didn't work for me.

I bought my laptop with Vista installed and later reformated and used Windows 7. During formatting with Windows 7 I had some problems with my hard drive and found out it was dead so I bought a new one.

I wanted to reformat with Windows XP,because Windows 7 is consuming more RAM that it is able handle and I wanted to use it for other programs. So I formatted with Windows XP Service Pack 3 but after first reboot a message appeared: "Error loading operating system"

Reading here, I assumed that maybe I had installed it on the wrong partition and maybe having two OS now, so I used fixmbr but it is still not starting up. Anyway I am sure that is not the case of two operating systems.

Is there any chance that when the computer designed to work with Vista you would face problems with Windows XP? Like not recognizing a hard drive?