Thank you for your response. I finally have an afternoon off where I can address the problem I'm having.
I had the problem with the D620 laptop where it would not boot up; not with my D610. When I start the laptop, my power light goes on, and the hard drive light will light up briefly, but then go out as the computer shuts down. I thought this was a similar problem I had with the D610 - it did not start, so I assumed a boot problem, and removed the removeable battery and the internal battery, then reassembled them. The D610 did restart properly. However, with my D620, this operation of removing batteries and then replacing them did not work, the laptop would still not go on.
I just had ordered a replacement mother board and installed it, with suggestion from others online that the Nvidia card may have destroyed mother board components. The laptop still will not work. The hard drive light will light for an instant, then go out as the computer shuts down. This would leave the hard drive, or perhaps the memory at fault.
Thank you for your advise. New developments, starting with an error on my part: since the system board came with a CPU heat sink, I didn't look to see if it was with a CPU! I found out it didn't have one, so I put mine in, however, upon start-up the laptop now only the shift lock and scroll lock lights flash for about a minute, then the unit shuts down.
Another blog says this may be a memory problem, where the RAM is not recognized.
I will remove one, and then exchange it with the other.