Well, that didn’t work.

You’re performing a fresh installation of Windows 7 on an older Windows XP Professional desktop PC, but the Windows 7 installation media won’t boot from the DVD-ROM drive and always boots Windows XP normally. The Windows 7 DVD-ROM boots properly on other computers in the office. What is the most likely cause of this issue?

Microsoft 70-680: 1.2 – Windows 7 Installation Sources

Most of us are accustomed to installing new software from a CD-ROM or DVD-ROM, but Windows 7 can be installed from many other sources. In this video, you’ll learn about Windows 7 installation sources and how you can create a bootable USB flash drive and a Windows PE boot disk.