Some detail needed.
You installed windows 10? From the DVD to blank disc?
When did you install Ubuntu?
Easy way is to first install Windows 10 to a MBR disk, shrink the partition and time. Windows 10 64 bit often uses GPT unless you tell it not to. install Ubuntu later.
How did you install Windows 10?
MBR is the common layout for hard drives that has been in use for a long time. Trying to do Ubuntu on the new GPT can require some more effort and research.
