unconstructable13 you're not meant to put ubuntu on a C drive, you're meant to make an entirely different partition during setup
ubuntu is meant to be on an ext4 drive, not a lettered NTFS drive
reinstall windows (if you still intend to dualboot), then try installing ubuntu again without partitioning within windows. you will see a screen that looks roughly like this

(note: this is an old image from like 2010 so take it with a grain of salt, original link)