Missing operating system

My Son's Asus A53S laptop has just yesterday come up with Missing operating system, I think it has automatically upgraded to windows 10 from seven and is now missing the boot sequence as it must have an Asus partition there for restoring win 7.

And no it was not backed up unfortunately!

So whats the best way to restore it back to win 7 as its his business PC.


I removed the hdd and plugged into another PC and its telling me to format the drive

I have accessed it in AOMEI partition Assistant

Disc 3 Basic MBR 596.GB = F: recovery 21.49GB G: 148.60GB H:425.64GB NTFS

So is there anyway to access this hard drive or is it locked in the Asus hdd configuration ?