I bought a 8GB kit from crucial and it came today. The kits has the same specs as my stock computer ram 4GB Kit but only slower memory speed. I installed them and computer would not turn on. I removed the old rams and the computer turned on perfectly and every thing is runs faster but only at 8GB I want 12GB. Why the old ram did not work with the new kit even though everything matches in specs and voltage, only the speed is different.? Now I think I need to buy the matching ram KIt from crucial. Could it had been the motherboard or the mix match branded ram or I put them in wrong?