Hace diez minutos que prueba la combinación del cofre.

Here hace is part of the time expression hace + period of time + que + verb.

In this pattern, it means:

someone has been doing something for X amount of time

So:

Hace diez minutos que prueba la combinación del cofre
= He/She has been trying the safe/chest combination for ten minutes

This is different from the more basic use of hace in:

Hace diez minutos = ten minutes ago

The full structure changes the meaning.

Because Spanish often uses the present tense for an action that started earlier and is still continuing now, especially in this structure:

Hace diez minutos que + present tense

So prueba does not mean only tries here in a simple present sense. In this construction, it corresponds to English:

has been trying

That is why Spanish does not need a separate present perfect continuous form here.

Both can be possible in Spanish, but they are not used in exactly the same way.

In this sentence, prueba is the normal choice because the structure hace + time + que + present tense commonly uses the simple present:

Hace diez minutos que prueba...

If you say Hace diez minutos que está probando..., it is also understandable and adds a stronger sense of the action being in progress right now, but the simple present is the more standard textbook pattern.

So:

• prueba = the usual form in this construction
• está probando = possible, with extra emphasis on the ongoing action

Spanish often leaves out the subject pronoun when it is understood from the verb form or from context.

Prueba can mean:

• he tries / is trying
• she tries / is trying
• you (formal) try / are trying

So by itself, the sentence does not tell you exactly who the subject is. You need context.

If you wanted to make it explicit, you could say:

• Hace diez minutos que él prueba la combinación del cofre
• Hace diez minutos que ella prueba la combinación del cofre
• Hace diez minutos que usted prueba la combinación del cofre

But normally Spanish prefers to omit the pronoun unless needed.

In this sentence, que is part of the fixed pattern hace + time + que + verb.

It does not translate neatly as a standalone English word here. You should think of the whole structure as one unit meaning:

for / has been ... for

So it is better not to translate it word by word.

Because de + el contracts to del in Spanish.

So:

• de el cofre → del cofre

This contraction is required.

Compare:

• la puerta del cofre
• la combinación del cofre

The only common exception is when El is part of a proper name, such as El Escorial.

It means the combination of the chest/safe, or more naturally in English:

the safe combination
or
the combination for the chest/safe

A few vocabulary notes:

• combinación here means a lock combination / code
• cofre can mean chest, strongbox, or sometimes safe, depending on context

In everyday modern Spanish, if you specifically mean a safe, many speakers would often say caja fuerte. But cofre is still understandable and can fit certain contexts.

Spanish uses definite articles more often than English.

Here la combinación refers to a specific combination: the one belonging to the cofre.

So Spanish naturally says:

prueba la combinación del cofre

where English might say:

tries the safe combination
or
tries the combination to the safe

The article sounds normal and expected in Spanish.

Yes. A very common alternative is:

Lleva diez minutos probando la combinación del cofre.

This also means:

He/She has been trying the safe combination for ten minutes.

Another possible version is:

Prueba la combinación del cofre desde hace diez minutos.

So Spanish has several ways to express this idea:

• Hace diez minutos que prueba...
• Lleva diez minutos probando...
• ... desde hace diez minutos

All are grammatical, though llevar + time + gerund is especially common in everyday speech.

Not in this full sentence.

On its own:

Hace diez minutos = ten minutes ago

Example:
Llegó hace diez minutos. = He/She arrived ten minutes ago.

But in your sentence, you have:

Hace diez minutos que prueba...

That whole pattern means:

He/She has been trying ... for ten minutes

So the meaning changes because of the full construction, especially que + present tense.

Yes, it is grammatical and understandable.

That said, in everyday speech many speakers in Spain might be more likely to say something like:

• Lleva diez minutos probando la combinación de la caja fuerte.
• Lleva diez minutos intentando abrir el cofre.

Why?

• llevar + time + gerund is very common in conversation
• caja fuerte is often more common than cofre if you mean a safe

So your sentence is correct, but depending on the exact context, a native speaker might choose a slightly different wording.