I am using an Acer Aspire One notebook, it doesn't have a CD/DVD rom so I used a bootable USB with the use of WintoFlash. The notebook currently have a Windows 7 Ultimate, but I want to downgrade it to Windows XP because it becomes slower when I used Windows 7. Note, I don't have any Windows.old on my system. When I reboot the laptop to install Windows XP, it goes well. But when it comes to the page where you can Select, Delete or Create a partition, the laptop's system drive is not showing. The page only shows the USB drive as my drive C, because it is my priority right? So now, I cannot reformat the laptop because the system drive of the laptop is not showing. What and where is the problem? Is it the bootable USB? or there is another way to make a downgrade? or the problem is my system drive? Please, help me and explain to me in the most simplest way!