User account disappeared

My Mac desktop hard drive became full and suddenly I noticed my user accounts disappeared. The only account left is the Guest account. Also even if I log in to the guest account, my admin account is not being recognized. I tried rebooting several times but the accounts does not come back. I cannot do much because my admin account is not being accepted. I tried to free up space and I was able to free 2 GB from my 1T hard drive. Problem still there.