This is because itunes automatically backs up, resulting in insufficient C disk system. The steps to solve the problem that disk C is full and cannot be backed up are as follows:

1 First of all, through the computer cleaning of 360 security guards, you can clean up the common garbage in drive C.

2. After cleaning up the common garbage, manage the contents of disk C by moving disk C, and open disk C to move.

3. Then transfer the important data in the C disk to other hard disks.

4. Then check the slimming function of the system disk. Slimming into the system disk is to solve the problem that the C disk cannot be backed up because it is full.