So you've lost the password to the root account. Worst, you've had a boot password and it was the same. Here are some instructions on how to get back into your system:
Create a user on another Unix / Linux operating system.
# useradd resetrootpass
then set the password on the new user:
# passwd resetrootpass
once password is set, edit the /etc/shadow file and copy the encrypted password text:
# cat /etc/shadow
to the /etc/shadow root's password field on your OS where you've forgotten your password too (You may need to use a boot CD like a Linux Live CD to mount the system with then mount the partition to get access to the /etc/ folder).
Once you replace the root's encrypted string with the new one you created above for an arbitrary user, you should be able to boot and login with the new password.