Boot nightmare

Hi to all,
I have a problem which I can't seem to fix. I have 2 laptops, both dvd drives are not working. I have an external Usb drive that won't work under boot up. Laptops don't recognise it until drivers are loaded.

The problem,

Hp pavilion dv6500 won't boot. Mbr is damaged. Can't use repair disk as won't recognise Usb drive.
So I put hdd into my other laptops 2nd hdd port " Hp pavilion Dv9800 and repaired boot sector that way. Tested it on dv9800 and boots fine.
Put hdd back into dv6500 and get same mbr fail message.

Please can anyone help?

Have you tried booting from a USB flash drive? I've seen many people have issues getting recent systems to boot from an external USB hard drive, but those systems should be booting from flash drives just fine.

That being said, it sounds like it would be worth your while to see about getting a replacement DVD drive from eBay or somewhere like that.

If the drive booted on one system but not another, that tells me there's a controller issue, or a BIOS option configured improperly.

I second Deacon's suggestion to write the Win7 Repair disk to a USB flash stick. I would try Win2Flash as it has worked for this before on Repair CD.
System Repair Disc - Create
YouTube - How to install Windows 7 from USB (WinToFlash)

Then boot the flash stick using one-time BIOS boot Menu key which on most HP's is ESC. Stick may be under flash or HD.

Make sure Win7's 100mb System Reserved boot partition is marked Active, or if you don't have it mark the Win7 partition Active, then run Startup Repair 3 times in case the MBR needs repair.
Partition - Mark as Active
Startup Repair - Run 3 Separate Times