They tried many things, but it did not appear that anything they tried was effective.

Many thanks for your help. Je comprends le sens de la phrase mais pas vraiment la grammaire/conjugaison utilisé. "Did + seemED"

I am a native English speaker but not a grammar expert, so I could be incorrect. "Nothing we did" forms a noun phrase that is headed by the indefinite pronoun "nothing." Sometimes you will see a "that" as in "nothing THAT we did." "seemed to help" follows the verb ("seemed") + infinitive ("to help") construction. "Seemed" is the past tense of the verb of perception (e.g. feel, look, etc.) "seem." Verbs of perception belong to the category of copular verb. The infinitive "to help" is functioning as a noun (a direct object of "seemed" in this example).

It's an odd expression, when I think about it. Essentially it means, "Nothing we did helped." I'm not sure why "seemed to" is added. Possibly there is still a slight chance that something we did will help or did help?

Ça veut dire qu’on a fait de son mieux, mais ça n’a pas marché.