不意をつかれて、私は一言も言えなかった。

、。

Caught off guard, I couldn't utter a single word.

Literal

Surprise [object-を] was-thrust [then-て] I [topic-は] one-word [even-も] couldn't-say.

一言も言えなかった uses 一言も with negative to mean 'not even one word.' The potential form 言えなかった emphasizes inability rather than choice. 不意をつかれて is the passive of 不意をつく ('to catch off guard').