Error "Setup was unable to create a new system partition or locate an existing system partition"

Hello,

Laptop: dell vostro n series laptop

I was trying to install windows 7 on my laptop by bootable usb. I tried to install several times but i recieved follwing result : "Setup was unable to create a new system partition or locate an existing system partition"

 In order to install i deleted my all partitons so I no longer have any OS in my laptop. So, I no longer able to use my laptop.

Please guide me how to install window on my laptop.