When you attempted to install Windows, did you try to install it to a separate partition than the partition that Ubuntu is on? Or did you simply try to install Windows to the whole hard drive and overwrite the Ubuntu partition(s) that you already had? This is very important. You may have inadvertently overwritten your Ubuntu install.
Boot from the Ubuntu live CD and load Ubuntu to the desktop. Open a terminal and run:
and post the output here. This will tell us if Ubuntu is still on your computer or not.
If you did install (or attempted to install) Windows to a separate partition:
1. Windows likes to be on the first primary partition. This is why it is recommended to install Windows first when dual booting Windows + linux. It is possible to install Windows to other partitions from what I have read. It is more complicated though.
2. When you install (or apparently even attempt to install) Windows to a system that already has linux, the Windows installer will overwrite the master boot record (MBR) and you will not get the grub menu when you boot your computer. To reinstall grub2 to the MBR see this:
The method to reinstall grub2 in the link that Lidex posted will also likely work.
Write back if you need more help. And please post the output of sudo fdisk -l
from the live CD.
And welcome to the LQ forums!