You havn't mentioned whether Ubantu inquired
about the grub settings during its installation or not. If Windows doesn't have the boot loader than you can manually check it by looking at the boot flag set at a particular partition. This can be done by using an open source media GParted
live cd, which can be used by booting from your CD Drive and then you can check and also set the boot flags at a particular partition. You can find it here:
After burning, boot from it and in the GParted
menu set the boot flag for the Ubantu
partition, then you can use your your Ubantu
, only if installed correctly, may be you can't use windows at that time, then remove the boot flag and windows will be back. Try installing Ubantu
again and check the settings for grub bootloader.