I installed Ubuntu 13.04 and then dual booted it with Windows. Now, when I boot into my system, the selection menu does not come up. Instead, it directly boots into Windows. Is there any way to have them both working?
Run Ubuntu Live from a CD, DVD or USB stick. Choose "Try Ubuntu" and when its loaded run the program "Boot Repair" from there. And fix the Grub..
That is why you usually install ubuntu after installing windows.
Try following the instructions here and it should help.