My iphone wont turn on: BLUE SCREEN?

IVE DROPED MY IPHONE4S So MANY TIMES IT HAS So MANY CRACKS IN THE BACK BUT IT WORKED FINE TILL ONE DAY I DROPED IT AND THE SCREEN CRACKED AND IT NO LONGER LET ME USE IT. IT GOES BLUE CANT DO ANYTHING I KNOW IT STILL WORKS CAUSE OBVIOUSLY IT STILL TURNS ON BUT BLUE SCREEN?

CAN ANYBODY TELL ME WHATS WRONG WITH IT THEY TOLD ME ILL HAVE TO REPLACE THE WHOLE FRONT PART ANYONE KNOW HOW MUCH ITLL COST ME?!

Hold the home and power button together for 15 secs then turn it on if it doesn't work them it doesn't work and your screwed: p