User name and password for gmail account

How do I get user name and password for my htc phone. I had to reset it, and it keeps asking for the original user name and password for my gmail account that was first synced with this phone. It has been changed a couple of times and can't remember the first account info. My phone number is **********. Can u help me with this problem? I can't my phone to work until I get this information. You can send any info to my dad's e-mail at ***@***.

Thanks Kenny Horn