So it depends on what order you installed everything, you might be able to repair, you might have to start over. I'll share some of my thoughts and if you can provide more details on how you set things up we can narrow down a solution for you.
The generally recommended sequence of installation is to prepare your partitions, install windows, then install linux so when grub2 configures it will find the windows bootloader and add to the grub menu. On machine's that come with WIndows preinstalled, you can shrink your windows partition using the Windows Disk Management utility from the Adminiistrative Tools section in the Control Panel, or you can just fire up a live linux disk/usb stick and use GParted as well.
If you install Windows second it likes to be the only OS on your system so will automatically bulldoze whatever grub files you had in the MBR. So in your case I hope you upgraded to windows 8.1 first.
As far as finding an existing windows bootloader and adding to your grub menu you could try using
os-prober which will do exactly what it sounds, probe your system for installed OSes and adds them to your bootloader.
It's always encouraged to read up on the documentation for your relevant problem. The Arch Linux Wiki is fantastically thorough and kept well up-to-date, the Grub section is here and another good resource is Dedoimedo's Grub Tutorial.
If your computer is a bit older then you likely should be installing the grub2 bootloader into partition containing the Windows MBR which is usually
If your computer is bit newer and has an efi boot partition then you can install one of the more recent Ubuntu builds like 14.04 and install your grub2 bootloader into the efi partition. This may vary by device depending on how your manufacturer set up the partition scheme. You should be able to see which partition is labeler "efi" using something like the GParted partition manager.
Newer Ubuntu-based distros seem to work well on efi machines. I've had good luck with stock Ubuntu 12.04+, Linux Mint 16+ and Ubuntu-Gnome 12.04+.
Another thing you can check is your machine's boot order in the EFI/BIOS settings. My EFI settings show both ubuntu and windows and I can adjust the priority of which will boot first. If you can see the Windwos bootloader in your EFI/BIOS menu then you might just need to use the
os-prober to add Windows to your grub, which would be the simplest solution.
Let us know how you fare.