It looks like you installed Ubuntu using the Something Else option, and you probably didn't notice a setting at the bottom that asks where to install GRUB (the bootloader). That setting was probably set to install GRUB on the root partition (
/) you chose, and not on the MBR. In turn, your Ubuntu installed successfully, but the current bootloader (the Windows bootloader) does not know anything about Ubuntu. You'll need to add an entry to the Windows bootloader to tell it "Hey look! There's another OS at this partition!"
Instead of doing that though, there's another easier (and a recommended way), which is to use the tool Boot Repair. Here's what you need to do:
- Boot your Ubuntu USB/CD, and choose the option to "Try Ubuntu", not Install Ubuntu.
Open a terminal Ctrl+Alt+T, and type the following:
sudo add-apt-repository ppa:yannubuntu/boot-repair && sudo apt-get update
sudo apt-get install -y boot-repair && boot-repair &
Once all of these commands are complete, the Boot Repair application should open up (if it doesn't search for it in the Dash (you can open the Dash by hitting the Windows key (or the Super key)).
In the application, hit Recommended Repair. This should fix your issues.
Please note down the URL that it provides you at the end (provided that you're connected to the internet). You can give us that link if something goes wrong.
Once done, restart, and you should see options to boot into Ubuntu or Windows. To test, boot into one of them. Verify it boots. Restart. Boot into the other. Verify it boots.
Post back that URL if something goes wrong.