Latitude D620 Memory Upgrade Problem

First time doing hardware changes to a laptop.

I got a used Latitude D620 a while back, installed Windows 7 on it and want more RAM.

What was in the machine:  2x "512MB 2Rx16 PC2-5300S-555-12" (1GB total).

What I purchased based on the seller indicating it was compatible:  2x 2GB "PC6300/6400 800MHz DDR2"

Both old and new are made by Hynix (coincidence).

Installed it and got the flashing Caps Lock light and no power up.  Reseated it a couple times, no change.  Reinstalled the original memory, worked fine.  Tried powering up with no memory installed, got the flashing Caps Lock & Scroll Lock lights and would not power up, so different than the first scenario.

I bought 4 sticks of this RAM, 2 for my laptop and 2 for another (Latitude D610) and tried all 4 in pairs and individually.  I can't believe all 4 sticks could be bad.

Could this be too much memory for this machine (despite numerous places claiming this range of memory is OK for the D620)?  Could it be too "fast" ?

I thought it would be like desktop RAM, only the same type will fit into the slot.  Am I wrong on this?

I Googled for a couple hours and found no help, or at least nothing that worked.

Thanks.