Viðhengið opnast ekki í vafranum mínum, svo ég prófa annan vafra.

Viðhengi is the noun meaning attachment. It is a neuter noun.

The ending -ið is the suffixed definite article, so:

• viðhengi = an attachment
• viðhengið = the attachment

In this sentence, viðhengið is the subject, so it is in the nominative singular. For this neuter noun, the nominative and accusative singular happen to look the same.

Opnast is the -st form of opna. This -st form is very common in Icelandic and often has a middle/passive-like meaning.

So:

• opna can mean to open something
• opnast often means to open / to get opened / to be openable

In a tech sentence like this, Viðhengið opnast ekki naturally means something like:

• The attachment doesn’t open
• The attachment won’t open

It sounds more like the file fails to open, rather than someone actively opening it.

In a normal Icelandic main clause, the negative word ekki usually comes after the finite verb.

So:

• Viðhengið opnast ekki = The attachment does not open
• Ég prófa ekki = I do not try

This is a very common Icelandic word-order pattern. English often puts not after an auxiliary like does, but Icelandic does not need that kind of helper verb here.

That phrase is in the dative.

The preposition í can take:

• dative for location: in
• accusative for movement into something

Here the meaning is in my browser, which is location, so Icelandic uses the dative.

That gives:

• vafri = browser
• vafranum = the browser in dative singular
• mínum = my in dative singular masculine, agreeing with vafranum

So í vafranum mínum literally means in the browser my = in my browser.

In Icelandic, possessives very often come after the noun, especially when the noun is definite.

So the normal pattern is:

• vafrinn minn = my browser
• vafranum mínum = in my browser

This is extremely natural Icelandic word order.

A form with the possessive first, like minn vafri, is possible, but it often sounds more emphatic, contrastive, or less neutral.

Here svo means so, therefore, or as a result.

It connects the two ideas:

• The attachment doesn’t open in my browser
• so I try another browser

Be careful, because svo can mean different things in different contexts, such as so, then, as, or such. In this sentence, it is a result connector: so / therefore.

Because prófa takes a direct object, and that object is in the accusative.

The basic dictionary form is:

• annar vafri = another browser
  nominative

But after prófa, it becomes:

• annan vafra = another browser
  accusative

Both words change:

• annar → annan
• vafri → vafra

So:

• Ég prófa annan vafra = I try another browser

Here it is a present-tense verb, not an infinitive.

That can be confusing because the forms look the same:

• að prófa = to try
  infinitive
• ég prófa = I try / I am trying / I’ll try
  1st person singular present

The infinitive usually appears with að. Without að, and after the subject ég, prófa is understood as the finite verb.

It can cover more than one of those in English.

Icelandic present tense is often broader than English present tense, especially in everyday speech. In context, ég prófa annan vafra can naturally mean:

• I try another browser
• I’m trying another browser
• I’ll try another browser

In this sentence, English would often translate it most naturally as so I’ll try another browser.

Because the sentence contains two full clauses:

• Viðhengið opnast ekki í vafranum mínum
• svo ég prófa annan vafra

In Icelandic, it is common to separate coordinated clauses like this with a comma, especially in clear written prose.

So the comma helps show the break between:

1. the problem
2. the result or response

It is mainly a punctuation question, not a change in meaning.