Why won't my phone turn on?

I have a BLU STUDIO M HD, recently i dropped it and it fell apart. I put it back together and turned it on. It worked just fine and that night i plugged it in and went to bed. The next day i couldn't get my phone to turn on and when connected to the charger its blu start up screen would flash on and go off. Sometimes just a grey screen would flash on and off. I tried just charging the battery and it's a 100%. I've tried a hard reset,but it won't do anything. Thanks for your help.