There is no alternative but then to create a new account, as you neither remember you ID, nor your password.
However you can try one last thing. On the website where you want to login, try looking for any of your posts in the forum or within any topics you had worked on. From there you can get your User ID link. Click on that & see if shows your mail ID over there. If yes, than well & good, else try getting in touch with admin to reset your password or something.
Else, go to the site users/members, & check if you can remember your user id & then follow the steps as the last statement I said.
Hopefully you might get it.
If not, then My friend, there is no other choice.
Hope this helps.