I bought a Dell Dimension 3000 and it came with Windows XP, and decided to upgrade it to Windows 7. After a few years, I now want to go back to Windows XP, simply because it is simple. My DVD Drive isn't working, nothing has been modified, or added, except one stick of RAM that is 1 GB I got from Staples. It works, and I know because I can run Win 7. I downloaded a retail edition of Windows XP Home Edition, SP3, the same OS my computer came with, and I have the licence key sticker attached to my computer. I put the Win XP installation on the USb by using Rufus. I then changed my boot to USB to default, and restarted my computer. Everything is working fine, and right when it says Setup is Starting, BAM! I got the Windows has been shut down to prevent damage. I looked around for a solution, and saw that I have to change my AHCI settings to IDE. I looked around my BIOS and didn't see any option for that. I have a Dell Dimension 3000 series BIOS, Intel Pentium 4 @ 2.8 GHz, !.25 GB of RAM, HIS Radeon 5450 512 MB Video Card, 200 watt power supply, and a 40 GB HDD. I would appreciate some help, and thanks.