Laptop no display

i didnot use my laptop for 15 days nd did not give charge as well though it did not have any charge so now i took the laptop and plugged in for charging.now the problem is when i tried to start my laptop,display did not come.the screen shows balck.i opened the battery and again set it but did not work.later i tried to press f8 ,first time it worked out but second time it did not come.Now what to do?please help me out.

Thank you