Change of Hard disk

Hi,

My Sony Vaio model no. sve151g13m had a corrupted 500 GB hdd which I wanted to replace, therefore, I bought another toshiba hdd of 1 TB, I downloaded windows image file from the internet and made my usb flash drive as a bootable drive with windows image file in it but when I start the system via assist and boot it from the external drive the windows setup doesn't start and shows OPERATING SYSTEM NOT FOUND instead.

NOTE: Currently I am residing in Pakistan, I bought this laptop from United Kingdom.

Please help me.

Regards.