Αν ξεχάσεις τον κωδικό σου, η εφαρμογή δεν ανοίγει.

Αν means if.

In modern spoken Greek:

• Αν and Εάν are practically the same in meaning.
• Εάν is a bit more formal or written; Αν is what you’ll hear most of the time in everyday speech.

Both introduce a condition, like English if:

• Αν ξεχάσεις τον κωδικό σου… = If you forget your password…

Ξεχάσεις is the aorist subjunctive, 2nd person singular of ξεχνάω / ξεχνώ (to forget).

Greek often uses the aorist subjunctive after αν for possible future events:

• Αν ξεχάσεις = If you (ever / at some moment) forget
• Αν ξεχνάς would sound like “if you are (habitually) forgetful / if you keep forgetting,” which is a different idea.

So:

• Αν ξεχάσεις τον κωδικό σου = If you forget your password (on a specific occasion)
• Αν ξεχνάς τον κωδικό σου = If you (tend to) forget your password (as a habit/personality trait)

Ξεχάσεις is:

• Aorist subjunctive
• 2nd person singular

In Greek, after αν in conditional sentences, the verb is typically in the subjunctive to express:

• Uncertainty
• Possibility
• A future event that may or may not happen

So:

• Αν ξεχάσεις… = If you (should) forget… / In case you forget…

The aorist aspect here focuses on the event as a whole, not on duration or repetition.

Greek almost always uses a definite article where English might not.

• τον κωδικό σου literally: the password of yours
  but it means: your password

Saying just κωδικό σου (without τον) is normally wrong in standard Greek in this position. With singular countable nouns, you almost always need the article when referring to a specific, known thing:

• το βιβλίο μου = my book
• η τσάντα σου = your bag
• τον κωδικό σου = your password

So the article τον is required here.

In Greek, possessive pronouns like μου, σου, του, της, μας, σας, τους usually come after the noun:

• ο φίλος μου = my friend
• η δουλειά σου = your job
• τον κωδικό σου = your password

Putting σου before the noun (σου κωδικό) is ungrammatical in this structure.

So the normal pattern is:

article + noun + possessive
→ τον κωδικό σου

Δεν ανοίγει is present tense, but here it has a general / habitual meaning:

• Αν ξεχάσεις τον κωδικό σου, η εφαρμογή δεν ανοίγει.
  = If you forget your password, the app (generally / in that situation) doesn’t open.

Greek often uses the present tense to express:

• General truths
• Regular results
• Rules and instructions

If you say:

• η εφαρμογή δεν θα ανοίξει = the app will not open (on that particular occasion)

That is also possible and correct, but it sounds more like one specific future event.
The given sentence sounds more like a rule or system behavior in general.

Η εφαρμογή δεν θα ανοίγει is grammatically possible, but:

• δεν θα ανοίξει (simple future) → a specific result: it will not open (that time)
• δεν θα ανοίγει (future continuous) → more like a repeated / ongoing situation: it will be not opening, it won’t be opening (habitually)

In practice:

• For a straightforward condition–result rule, Greek would prefer either:
  • η εφαρμογή δεν ανοίγει (present, general rule)
  • η εφαρμογή δεν θα ανοίξει (simple future result of that condition)

Δεν θα ανοίγει is less natural here unless you’re emphasizing ongoing or repeated failure over a period of time.

Greek is a pro-drop language: subject pronouns are usually omitted because the verb ending already shows the person.

• ξεχάσεις clearly indicates “you (singular)”.

• Adding εσύ (you) is only needed for emphasis or contrast:

  • Αν εσύ ξεχάσεις τον κωδικό σου…
    = If you forget your password (as opposed to someone else)

In a neutral sentence like this, εσύ is normally omitted.

Κωδικός (code / password) is masculine.

You can see this from the article and the ending:

• τον = masculine singular accusative article
• κωδικό = accusative singular of κωδικός

So:

• ο κωδικός (nominative, subject) = the code / the password
• τον κωδικό (accusative, object) = the code / the password

In the sentence, τον κωδικό σου is the object of ξεχάσεις.

Greek has two common words that can both appear as “application” in English, but they mean different things:

• η εφαρμογή
  
  • software / app
  • a program on a phone, computer, etc.
• η αίτηση
  
  • an application form / request
  • e.g. a job application, a visa application

Here we’re talking about an app that opens or doesn’t open, so η εφαρμογή is correct:

• η εφαρμογή δεν ανοίγει = the app doesn’t open.

Δεν ανοίγει literally means “(it) does not open.”

• ανοίγω = to open
• ανοίγει = he/she/it opens

It works similarly to English:

• Ανοίγω την πόρτα. = I open the door.
• Η πόρτα ανοίγει. = The door opens.
• Η εφαρμογή δεν ανοίγει. = The app doesn’t open.

So using ανοίγει with η εφαρμογή is natural Greek for software not starting or not loading.