Pavilion does not recognize 2nd RAM chip

I bought NB w/ two 512 mem chips, then bought & installed two 1GB chips. Computer reports only 9xx MB memory. I'm sure there is an easy way to correct this, but I don't know it. I'm also sure that you can tell me how to do it. Thank you. doctorj

 

what model pc, the best way to get ram is to go to crucial.com plug your make/model into there ram finder thing, it will tell you what type is compatible with your machine. then you either buy it there or look around for the same type