I recently had to put my laptop in to a repair mode where it recovered all the files on the computer, but not the apps or settings not really sure why, could have been a virus? 
Since then I've been getting problems where I turn on my laptop and it says 'Operating system not found' but when I reboot Windows will configure and then everything will be as normal and run fine. I also sometimes get crashes error:KERNAL_DATA_INPAGE_ERROR (fastfat.SYS) but after restart the computer is fine.

Model is: SVE1512W1ESI

Could you advise me on how I can fix these problems? 

Many thanks.