Moniter not receiving signal

(I should preface this with the fact that I dont know much about computers but I know a little bit)So I started building my own pc and I finally put all the pieces together and I plug it into my moniter (an acer H236HL). It "scans" all its ports and after a few seconds displays the message "no signal". (BTW I don't have an operating system installed) After a while I take it to my local computer place and they take a look, find out all I need to do is swap around the ram sticks. Once they're switched they say it boots up fine and I take it home. Of course the first thing I do is plug everything in boot up the computer and all I get is the "No Signal". So I'm hoping any of you guys know the problem and can give me a quick fix. Thanks!