Upgraded ram is showing but unusable.

I have Acer Aspire E15 E5-553 laptop which has two slot with total DDR4 4GB memory. I have replaced one memory with crucial DDR4 4GB 2133 MHz laptop ram. Total memory shown in bios is 6GB. But when I see ram information in control panel of the windows 10 it is showing that 2GB is in used out of 6 GB. Moreover, when I removed all RAM and using only the replaced RAM the computer do not start and bios screen also not shown. What is wrong? Is the Crucial RAM is not compatible with my computer? Appreciate your help.