Well...Since Windows Vista, no ntldr file is used, and instead of it, the bootmgr file has taken its place...
My guess is that you're either booting to the wrong CD/DVD drive, or your BIOS has some unsupported settings.
The Windows 7 DVD contents should have only a setup.exe file, a bootmgr file, a readme.txt file perhaps and some folders, support, boot, efi, etc. If this is your DVD contents, then your BIOS has some wrong settings.
Try changing the boot order in your bios and/or resetting your BIOS to defaults.
To enter BIOS, in most cases you need to press DEL key or F2-F10 key at computer's first startup screen.
Hope it helps