Make sure you have installed the ram in slot 1 and slot 3 of the four slots if you have them.
Make sure the ram is pushed firmly in until the white clips click into place as they can take a bit of pushing.
If ok,could be a bad stick.
Also check your temps in the bios as it could be cpu or motherboard overheating.
Or download and install
Could also be a failing psu as well,although sinse the ram was the last thing you did,then the ram is favourite.
What motherboard do you have?