Put the back cover back on but don't yet close the plastic clips or screw in the screws.

Firstly, boot up the computer while hitting F2 to open the BIOS configuration.

Check if the detected memory matches with what you have installed.

If it doesn't, you may have to take out the ram and put it back in again, making sure it really is all the way in.

Turn off the computer by hitting the power key.