Let’s take another example. ‘I command you not to attack before dawn,’ the general ordered his troops would be reported as The general ordered his troops not to attack before dawn. However, what if the original was ‘I command you to not attack before dawn,’ the general ordered his troops? To be faithful to the general’s words, wouldn't that have to be reported as The general ordered his troops to not attack before dawn?
The problem is with the type of catenation patterns help governs.
Many verbs in English catenate (form allowed strings):
He sat reading.
He started to cry.
He helped wash up.
He helped to wash up.
He helped us wash up.
He helped us to wash up.
There are several patterns, and different patterns are allowed for different verbs.
"He tried to help me learning..." has a string of three catenated verbs, with an interposed object (me). The first catenation (He tried to help [me] ) is fine - tried catenates with a to-infinitive, as here, or an -ing form (obviously, the -ing form has to be nearer the verbal, participial, end of the spectrum for catenation of verbs to apply - see below). They have slightly different meanings.
However, help normally catenates with a bare infinitive or to-infinitive, so "He tried to help me learn..." or "He tried to help me to learn..." would be used.
Help does catenate in one construction with an -ing form: I can't help loving you - but help here means avoid / give up.
Help also appears in similar-looking constructions with more-nounal -ing forms: This drug is given to help breathing.
A good article is at http://en.wiktionary.org/wiki/Appendix:English_catenative_verbs - although the 'present participle/gerund form' mysteriously suddenly narrows to the 'gerund form'. The Quirk umpteen-point gradience along the verb - noun continuum for -ing forms is, I believe, a more accurate model, so I prefer the cover term '-ing form'.
That's the grammar, but using the infinitives loses the progressive sense. A rewrite would be:
I was learning English - and he was trying to help me.
Or, if we do not wish to stress a continued duration of the attempt to help:
I was learning English - and he tried to help me.
Best Answer
Grammatically, all the sentences are correct.
There are usually differences in implication depending on context. Subtle changes in meaning can be imparted by what is called semantics.
Note also that some forms/ constructs may be idiomatic in some places but not in others. So what sounds natural to some people may be odd to others. It is important to know the target audience in selecting the form of the sentence that suits best.
In many languages, grammatically similar sentences with different word order/ construct can also have different meanings, defined by usage and custom rather than language per se.
Say, for instance:
"Help my sister peel oranges." could suggest "show her how to do it"
"Help my sister to peel oranges." might imply "prepare the oranges so she can peel them"
"Help my sister peeling oranges." can indicate "I mean the one who is peeling oranges, not the other"
"Help my sister with peeling oranges." maybe seen as "do half the work"
None of these interpretations can be drawn, though, without knowing the cultural and pragmatic context.
Other prepositions …