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.
I figured that it had to do with the BIOS performing a full memory test. If the operating system boots up and shuts down properly, the BIOS will only perform a quick test and move on. In all other cases, a thorough test will be performed to ensure functional RAM. Unfortunately, large RAM sizes make this thorough test incredibly lengthy, even though your RAM may be perfectly fine.
There is a BIOS setting that allows you to choose between “Auto”, “Minimal”, and “Thorough”, but in reality “Auto” and “Minimal” are the same thing – I still have mine set to “Minimal” and it runs into the full memory test whenever the BIOS detects an abnormal shutdown.
I performed memory tests later, using memtest86+, to rule out memory issues. The RAM passed 100%. After being fed up with the nonsense memory check the BIOS seems to have a fetish for, I started to hunt for solutions. Out of a combination of disassembling the BIOS, Google-ing, and contacting Dell’s tech support (which didn’t help at all), I found that you can press the space bar during that full memory test and it will bypass it for you.
Again, this is undocumented, except for 1 or 2 very old forum posts out there that suggested this workaround for much older models. Apparently it still works. So the next time you get stuck, try pressing that space bar.
Now Dell, why wouldn’t you tell your customers about this?