When using two sticks of ram in a laptop, it is always best to use identical sticks. Mixing and matching leads to problems. Still, sounds to me like either one of the sticks is incompatible with the computer or has gone bad. Try booting one at a time. If one can boot the computer alone and the other can't then you have found your culprit. Also, never ever install a ram module into a booted computer. It should be uplugged with the battery out anytime you make changes to the ram