No power. We just put a new battery in our computer, the only thing that would come up was a

Question

We just put a new battery in our computer, the only thing that would come up was a black screen saying operating system not found. We started to get it to work and now the computer just shut down and we cannot get it to come back on. We plugged in the ac adapter but there are no lights coming on and staying on. The red light comes on and blinks 4 times and goes off again. Any ideas?