Check if your RAM Slots are colored. If they are, the 2 sets of 2GB RAM should be put in slots with the same color.
If the slot arrangement is like 1(Black), 2( White), 3(Black), 4(White), 5(Black), 6(White)....... then
Put 1 2GB module in slot 1(Black) & the second one in slot 3(Black). This should be the most common arrangement for multi channeling.
But if there are no color indicators, better check the MOBO Manual.