Hello and Welcome to LinuxQuestions,
Normally it should be root (found that on Google). If for any reason it's no longer that then you might try to reset it. You could try rhe procedure listed here in this post at LQ
. Never used PCLinuxOS but if you're logged in as the only other user and you're in the sudoers list you could try providing your password or become root using
and typing your password. Once you're logged in as root in the terminal using the above command type
and provide the new password for root. Hope that helps. Have fun with Linux.