Nie ma sensu zgadywać hasła; lepiej spokojnie zadzwonić do biura.

This is a very common Polish impersonal pattern.

• nie ma sensu = there is no point / it makes no sense
• then comes an infinitive: zgadywać = to guess

So Nie ma sensu zgadywać... means There is no point in guessing...

Polish often does not need a dummy subject like English it or there. English says There is no point; Polish simply says Nie ma sensu.

You can use the same pattern with many verbs:

• Nie ma sensu czekać.
• Nie ma sensu się kłócić.
• Nie ma sensu próbować.

Because sens is affected by negation after ma / mieć.

Compare:

• To ma sens. = That makes sense.
• To nie ma sensu. = That doesn’t make sense.

In standard Polish, the object of mieć often changes to the genitive under negation. So:

• positive: ma sens
• negative: nie ma sensu

That is why you get sensu here.

This is an aspect choice.

• zgadywać = imperfective
• zgadnąć = perfective

Here the idea is trying to guess, guessing away, or making guesses, not one completed successful guess. That makes the imperfective zgadywać natural.

So the sentence suggests:

• don’t spend time guessing
• instead, make one sensible phone call

If you used zgadnąć, it would sound more like to guess it correctly once.

Formally, hasła can be more than one thing:

• genitive singular of hasło
• nominative/accusative plural of hasło

So by form alone, hasła is ambiguous.

In a sentence like this, context or the translation shown to the learner tells you which is meant.

Useful forms of hasło:

• singular nominative: hasło
• singular accusative: hasło
• singular genitive: hasła
• plural nominative/accusative: hasła
• plural genitive: haseł

That is why learners often pause at this word.

If the intended meaning is singular, then hasła is genitive singular.

In negative environments with infinitives, Polish can use the genitive for the object, especially in more formal or standard phrasing. So a learner may encounter:

• Nie ma sensu zgadywać hasła.

Even though the basic direct object of zgadywać is often thought of as accusative, the wider negative structure can pull it toward the genitive.

This is one of those places where Polish case usage can feel less straightforward than English.

Lepiej by itself often works as an impersonal recommendation:

• Lepiej poczekać. = It’s better to wait.
• Lepiej zadzwonić. = It’s better to call.

So lepiej spokojnie zadzwonić do biura means better to calmly call the office.

You could say jest lepiej, but that usually means it is better in a different sense, not necessarily giving advice.
You could also say byłoby lepiej, but that sounds more hypothetical: it would be better.

Because spokojnie is an adverb, and it modifies the verb zadzwonić.

• spokojny / spokojna / spokojne = adjective = calm
• spokojnie = adverb = calmly

So here it describes how to call:

• spokojnie zadzwonić = to call calmly

It does not describe a noun, so an adjective would be wrong here.

Again, this is aspect.

• dzwonić = imperfective
• zadzwonić = perfective

Zadzwonić suggests one complete call: make the call, get it done. That fits the advice in the sentence.

So the contrast is neat:

• zgadywać = keep guessing / be in the process of guessing
• zadzwonić = make one call

Polish often uses this kind of aspect contrast to show which action is vague/ongoing and which action is a single practical solution.

After zadzwonić, Polish normally uses do + genitive for the person or place you are calling.

So:

• zadzwonić do mamy = to call Mom
• zadzwonić do lekarza = to call the doctor
• zadzwonić do biura = to call the office

Biuro is a neuter noun, and after do it becomes genitive:

• nominative: biuro
• genitive: biura

So do biura is required by the preposition do.

Because the sentence has two closely related independent parts:

• Nie ma sensu zgadywać hasła
• lepiej spokojnie zadzwonić do biura

A semicolon links them neatly and shows a stronger break than a comma, but a closer connection than a full stop.

A plain comma would usually be considered wrong here unless you added a conjunction. For example:

• Nie ma sensu zgadywać hasła, więc lepiej spokojnie zadzwonić do biura.

Without więc or another linker, the semicolon is a good choice.

Yes, Polish word order is flexible, but the original is neutral and natural.

• Nie ma sensu zgadywać hasła; lepiej spokojnie zadzwonić do biura.

That order presents:

1. the bad idea
2. the better alternative

You could move things around for emphasis, but the tone would change. For example:

• Lepiej zadzwonić spokojnie do biura — possible, but slightly different rhythm
• Hasła nie ma sensu zgadywać — much more marked, with emphasis on hasła

For a learner, the original order is the safest model to copy.