Hp laptop will not boot

Hello,

I've recently opened my hp laptop to add additional ram to it. It worked perfectly afterward, but when i re-opened it to show my friend how i did it, it wont turn back on after closing it up. I tried taking off the battery and holding down the power button for 45 sec and it worked at first. But when i turned it off it wont turn on afterwards. I re-tried the procedure but it didnt work this time. Help needed..