Exactly what happens when you try to boot into the Windows 7 DVD or Repair CD? How to Boot your Computer from a Bootable CD or DVD
If it won't boot that way, enter BIOS setup to reset to defaults, then set HDD first to boot, trigger the DVD drive using the one-time BIOS Boot Menu key given on first boot screen.
Next try writing the latest official installer for your licensed version to flash stick, booting that, using Steps 1 and 2 from Clean Reinstall - Factory OEM Windows 7
Fill in your System Specs in bottom left corner of post.