If your cPanel/WHM has expired and you are not able to create new account from WHM panel although you have root access to the server, you can still create and use new accounts via SSH. Lets do it now.
Follow below steps to add/create new cPanel account from SSH:
Login to SSH via Putty or any SSH client with root access
execute following command:
/scripts/createacct domain user pass quota cpmod ip[y/n] cgi[y/n] frontpage[y/n] maxftp maxsql maxpop maxlst maxsub bwlimit hasshell[y/n] owner plan maxpark maxaddon featurelist contactemail