I had purchased software to uninstall programs and files from my computer. It was a non-MS program. It caused some features to glitch. I got out my XP OS disk and proceeded to reinstall XP. Well, after doing so, the computer would not recognize that my modem. I reinstalled it again, and selected it to switch the hard drive to NTFS format. I later learned that it could not be reversed, and that XP could not be uninstalled after the switchover. I took my computer to the place I had it built and had them reformat the hard drive and reinstall XP only with the FAT32 drive format.