My laptop does not start

I have a latitude e5440 with 4g ram. I wanted to add another 4g ram (from an inspirion dell) to my latitude. I add the ram and start my latitude laptop, but windows just recognize 4g ram. Then I removed 4g ram of latitude and start the laptop with the 4g ram of insprion. The laptop did not start-up. Then remove the 4g of inspirion, and put the same 4g of the latitude and start the laptop. But it does not start-up. When I push the turn on bottom, it turns on and after less than 2 second it turns off.