1 is correct. You can optionally omit ‘by’. The wording ‘at hand’ is good but rather formal. More colloquially would be something like ‘Nobody else was around so I had to do it (by) myself.’ The ‘by’ suggests that it would be more normal for more than one person to do it at the same. Without the ‘by’ you are emphasizing that you are doing something and not someone else. Both are correct. I’m just clarifying the difference in meaning.

correct: #1. All others have mistakes: #2: I had to do it by myself for there SEEMED to be nobody else at hand. #3: I had to do it by myself, there being nobody else at hand. #4: I had to do it by myself with nobody else at hand.

#1 is definitely best. It is grammatically correct, and it sounds natural. #2 sounds like you chose to do it so you could be alone, but it is grammatically and syntactically correct. I'm not sure about #3 in technical terms, but it sounds strange. #4 is definitely incorrect.