Thanks guys for your help.I'm bit late to inform you that everything is working fine now.You guys rocks.
Black screen problem was mainly for lack of nvidia driver.I installed the driver and everything is fine now.
But i need to change my battery.
.It's showing "consider replacing your battery."
I cross check it with HP battery health check up software and it is also showing the same that my battery has lost it's storage capability.So i think i've to change my battery.
I'm using 6 cell battery.What is the difference in backup time with 9 cell or higher cell battery?I want to know that those battery will be compatible with my laptop or not?