If you get the same result with the hard drive out as when it is in, then I would be inclined to agree that it is probably not the hard drive. If you have the time, another way to go about this would be to pull all the easily removable components (memory, wireless card(s), hard drive, optical drive, battery) and put them back in one at a time and testing the system until the problem comes back (D610 service manual). This might allow you to figure out which part is causing the problem. With all those parts removed you should get a memory error, but if it does the same thing as it does now, then its almost sure to be the motherboard.
I'm pretty sure the default Ubuntu LiveCD will allow you to mount the Windows partition so if nothing else you might be able to back up your data that way. Pulling the drive and using it in an external enclosure on another computer is another way to try and recover your files.