、。
I'm just a weak, powerless human being.
Literal
Fragile [copula-で] power [attributive-の] not-exist, just [attributive-の] human is-[explanatory-んだ].
脆弱 ('fragile, frail') is a formal/literary word, more so than 弱い. The relative clause 力の無い uses attributive の instead of が — a standard rule: in noun-modifying clauses, が may be replaced by の. The copula で here links the first adjectival clause to the following relative clause. ただの 'just a, a mere' downplays the following noun. ~んだ is the explanatory/assertive sentence-ending.