Are you sure your DVD drive is in working order (ie can you read discs with it in Windows) ?
If it's not shown as a boot device in the boot menu then it may be faulty and the laptop is not detecting it.
Start Windows 7 and check to see that the DVD drive is showing in the drives window.
If it isn't, check to see that the drive itself is flush with the laptop edge.
If it's sticking out even a small amount it won't be connected properly.
Give it a firm push so it doesn't stick out.
That happened on my son's laptop - the CD drive was sticking out - it wasn't being detected. So I pushed it firmly in and that cured it. It happened when he dropped it on his bedroom floor although miraculously nothing was broken, not even the hard drive.