I installed 16GB of ram into my Precision M6400 the other day and it things ran perfectly fine, until I had to force an ACPI shutdown by holding the power button.
When I turned it back on, the progress bar on the BIOS’s POST (power on self test) screen (big dell logo) got stuck at about 80% and started crawling for about 15 minutes before it moved on with the boot process. In my case, it was to ask for a biometric verification. But since it took so long to start up, I went to go do something else. By the time I got back, the laptop had turned itself off again because no credentials were provided to continue the boot process. So I turned it on again and had to wait out the full 15 minutes.