Your install was probably fine. But odds are you chose a (somewhat) manual installation and installed Grub (the bootloader) to the wrong device. If you're up for a retry: go the fully-automatic route with the installer. You can try it in a VM first. Just set up VirtualBox on your Windows machine and install Kubuntu to a virtual disk. That way, you can figure out what may have gone wrong. And if shit hits the fan again: you still have a functional operating system, reset the VM and go again.