Remove the new RAM sticks you installed and put back the old ones. Try again.
If it worked, the new RAM you used were not compatible to your computer. If it didn't, turn off the computer, press the RAM sticks down to make sure they're firmly seated in place then wiggle them a bit from side to side to make contact. Turn on. If that didn't work, turn off, remove all RAM sticks and with an eraser (the one at the end of a pencil), clean the gold contact points making sure you don't rub it on anything else. If that still doesn't work, bring the computer to the service center.