Yeah dude... when you upgraded your Ubuntu, it reinstalled the Grub (Windows equivalent of the Boot loader). You probably have your Windows on a weird partition so the default Grub partition doesn't find Windows anymore. Given the number of ways you can setup your loader though, there could be other explanations, but I'm sure it's your loader. When you start your computer at the OS selection screen, is it Grub? or Boot loader? If it's Grub, there should be an option to "edit" your boot config... in there, just simply modify the partition (e.g. "hd0,1" where the first number represents the physical drive and the second the partition number on that media. Only fiddle with the numbers, not the hd in front because it may be different depending on what type of hard drive you have :D ), don't worry the changes here aren't permanent so it's safe to experiment. Once you figure out the correct partition where your Windows Boot loader is located, you can make these changes permanent within your Ubuntu terminal. Good luck, and cheers!