Sometimes people place their rear channels a little too high or too far back for optimum effect. But thats ok, you can just adjust the gain to compensate. I placed in good spots & still turned them up a bit. I like to know they are there; I like the surround experience.
first of all, verify that you have your rear channels plugged in correctly. The brute force way to do this is by playing a dvd that has surround sound.
Assert that surround sound is selected in the dvd setup/language menu, sometimes its called dolby 5.1 or dolby digital (also DTS, but very rare & not supported by all players/receivers).
Go stand back by your rear channels & see if you hear ANYTHING come out of them. If so, then just adjust the gain on your rear channels. Do this with your receiver.