To solve this problem you need to Uninstall grub menu(Remember formatting ubuntu or linux will not work) and then reinstall.you need to uninstall grub menu and then reinstall this is the onl;y solution for it.
take two pen drive and make bootable of windows and Linux both
then to uninstall grub menu
first of all make a windows bootable usb disk with the help of windows setup img file(win 7,8,10,any one) with the help of rufus then start with the usb boot your computer then start with installtion process click next there you will seee repair your computer click on that and then select troubleshoot then select command prompt
and type one by one
remember – no data loss will happen
This will uninstall Linux Grub menu