No bootable devices found

My dell Vostro 3510, is giving me the " No bootable devices found " 

I have tried this:How to repair the EFI bootloader on a GPT Hard Drive for Windows 7, 8, 8.1 and 10 on your Dell personal computer | Dell US

 With this one using the command bootrec /fixmbr  I got the access denied error.

I also tried this one

 https://www.dell.com/community/XPS/no-bootable-devices-found/m-p/7530614#M58934 

I don't want to reinstall Window,  please help

Thanks