While accessing WHM you may get 500 internal server error. This can be the issue with either disk space or inode limit. You can solve this by using below steps:
Step 1: First check if the disk space is full. You can check this by login to putty.
Login to putty shell and run command “df -h”.
Step 2: If it is 100% full then check which folder is consuming more disk space.
Go to shell and go to directory by typing cd and run command du -sh *
Step 3: If it is not the issue with diskspace then check the inode limit using the command df -i
If it is the issue with inode then you need to free up the space by deleting backup and emails from server.