Why system drive do not appear when reformatting/ changing operating system?

[putrakla99]

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!

 

[weaselman]

You obviously have an interface that windows xp cannot see.
You should check in the laptops bios if there is a way to change the type of interface Ie: Sata,Ahci,Ide. If the drive is set to use the Sata interface then it is likely that it requires a sata driver to be installed first by pressing the f5 option on windows xp to load the drive so the HD can be seen.
Or simply change the HD mode in the bios if you can to AHCI mode.