it occurs over time but you may notice it all of a sudden.  it may have nothing to do with restart.  3,4 lights according to menu means “Memory modules are detected, but a memory failure has occurred.”  If you are 100% sure you inserted memory correctly in DIMM 1 using proper technique, then there is not much you can do.  I would just insert it a couple more times to confirm.  I like to hear a simultaneous snap from both retainer tabs of DIMM slot when I insert memory to confirm even pressure.
First off, I know this is an old system, but I found something really weird. 1 Ram slot works, I tested the 2 ram dimms and they both work in slot 2. Anything could be causing this? Love some help.
Optiplex 380 1 Ram slot works