First of all you upgrade your grub.
If the above command didn't work,
Then you download a windows iso file and also install 'winusb' application which is used to make bootable images of windows, if you have a cd it's fine.
Remember the partition name of your ubuntu.
Now you from from windows usb or cd. Now you click on repair this pc and troubleshooting startup options.
It will automatically replace your grub and now you will be able to boot into windows but not into ubuntu.
Now you either install a brand new ubuntu or try working around with reparing it.
If you are going to install brand new ubuntu then i would suggest you to install the boot-loader(Grub2) on the root file system itself.
Then you install EasyBcd application for windows and then link the boot loader to the ubuntu partition, as this the safest way to go on, so that if you have any updates of grub or windows boot-loader there wouldn't be any trouble for you in future.
Click here To watch a video about installing in the safest way.
I have installed 5 Linux Systems and 1 Windows os using the method mentioned above, I haven't got any problem till now.