|Is Windows 7 DVD a "factory" DVD or a copy ?|
If it's a copy
- it may not have been made properly (it's not bootable) , in which case the DVD will NOT boot the system on ANY computer. E.g. try to boot your laptop with it.
(The *.img file that makes the DVD bootable is not visible in Windows - if you use "Disk at Once" or similar in a burning program to copy the entire Windows disk, that hidden file is copied, but if you copy the contents of the Windows disk, it is NOT copied . You must have Windows Folder Options set to show all hidden files and folders before you make the copy. )
- the same applies to copying the contents of an actually bootable Windows 7 DVD to a flash drive - you MUST do that the right way, otherwise the USB drive will NOT be bootable. Try the USB drive that you copied the DVD contents to with another computer - I suspect it probably will NOT boot the system on other computers capable of booting from a USB drive either.
(The procedure for making a USB drive bootable is different.)
- a DVD-R burnable disk should read fine in any drive capable of reading from a DVD, but other types of burnable disks may NOT read properly in a drive it was not made in, and/or may NOT be found by the bios to be bootable in that case.
Are you SURE the drive you're inserting the DVD in can read DVDs ? If It can't, the bios will NOT find a bootable disk.
Is the optical drive you're inserting the Windows 7 DVD in new or used ?
If it's used, the laser lens may be "dirty"- if it is "dirty" that can prevent the disk from being detected as bootable. Use a laser lens cleaning CD in the drive. If you don't have one, get one, you should have one. Most places that sell CDs and DVDs have them, or even some "dollar" stores have them for a buck or two.
An optical drive does not necessarily have to be first in the Boot Order or similar settings in the bios Setup in order for you to be able to boot from a bootable optical disk - it just has to be before any hard drive.
You can have problems with a data cable that results in a bootable optical disk not being found bootable.
It is common to un-intentionally damage IDE data cables, especially while removing them - the 80 wire ones are more likely to be damaged. What usually happens is the cable is ripped at either edge and the wires there are either damaged or severed, often right at a connector or under it's cable clamp there, where it's hard to see - if a wire is severed but it's ends are touching, the connection is intermittant, rather than being reliable.
Another common thing is for the data cable to be separated from the connector contacts a bit after you have removed a cable - there should be no gap between the data cable and the connector - if there is press the cable against the connector to eliminate the gap.
80 wire data cables are also easily damaged at either edge if the cable is sharply creased at a fold in the cable.
Try another data cable if in doubt.
Check your SATA data cables. The connector on each end should "latch" into the socket on the drive and on the mboard, or on the drive controller card - it should not move when you merely brush your hand against it near the socket - if it does, mere vibration can cause a poor connection of it - use another SATA data cable that does "latch", or tape the connector in place.
(There is a slight projection or bump on one side of the outside of the connector that "latches" it into the socket - it's easily broken off or damaged)
The same thing applies for the SATA power connection.