My MacBook Wont Startup. Please help.

Hello Apples.

I have a problem. I have a Macbook Air (installed Os X El Capitan few days ago).

When I trun the laptop on, the apple logo appears , but it wont start.

I tried to Cmd+Alt+P+R and repaired the Disk Utility, but still cannot start up.

I also tried to reinstall the Os x but it did not work.

Then I wanted to boot but... it shows Waiting for DSMOS.

Please help me..

Thanks