Both the sentences you have provided are definitely not correct grammatically. If you heard someone say this in conversation, it may well be that this misspoke, or you misheard.
The closest sentence which makes grammatical sense that I can think of is:
It's as hard as nails for me to want not to do anything about it.
As you correctly identified, the extra 'to' to create the infinitive 'to do' is definitely needed.
The phrase 'as hard as nails' is not very natural in this context. 'Hard as nails' usually means something that is physically hard, not difficult. Someone can be 'hard as nails' if they are tough and strong. A desire to do or not do something can be 'hard' but not usually 'hard as nails'.
And finally, if you were writing this from scratch I'd avoid 'to want not to do' ... it's a clumsy sort of phrase and the placing of 'not' is awkward. You'd be better to say:
It's hard for me not to want to do anything about it.