The red bar is in no way related to the re-seating of your RAM.
That is a VERY full drive and Windows is letting you know that you either need to move some data to a different drive or upgrade the main boot drive to a larger disk. When drives get that full they begin experiencing noticeable slowdown, so before long you'll see some performance drop.
From the looks of the picture you do have a data drive, so it would be a good idea to migrate some non-critical material from your boot drive when you get a chance.