Why does the task manager show that C drive is full, but I have over?
If by task manager you mean Windows 10 Task Manager, take a closer look at the two disk-related graphs; how are they labeled? Active Time and Disk Transfer Rate. Neither has anything to do with how full they are. To see how full your disks are, go into Windows Explorer, click My Computer, and expand devices and drives. That will show you numbers and bar graphs showing how full your disks are.