Festplatte und Cloudspeicher verhindern den Datenverlust.

Because the subject is Festplatte und Cloudspeicher — two nouns joined by und. In German, that makes the subject plural, so the verb must also be plural:

• Die Festplatte verhindert den Datenverlust. = singular subject
• Festplatte und Cloudspeicher verhindern den Datenverlust. = plural subject

Even though each noun is singular by itself, together they count as more than one thing.

Because Datenverlust is the direct object of verhindern, and verhindern takes the accusative case.

The noun Datenverlust is masculine, so:

• nominative: der Datenverlust
• accusative: den Datenverlust

So in this sentence:

• Festplatte und Cloudspeicher = subject
• verhindern = verb
• den Datenverlust = accusative object

These are compound nouns, and in German the last part of the compound determines the gender.

• Festplatte ends in Platte → die Platte → die Festplatte
• Cloudspeicher ends in Speicher → der Speicher → der Cloudspeicher
• Datenverlust ends in Verlust → der Verlust → der Datenverlust

This is a very useful rule for German compound nouns.

Because German usually writes compound nouns as one single word.

So:

• Fest + Platte → Festplatte
• Cloud + Speicher → Cloudspeicher
• Daten + Verlust → Datenverlust

English often separates these ideas into two words, but German usually combines them. That is one of the most common differences English speakers notice.

Because in German, all nouns are capitalized.

So here the nouns are:

• Festplatte
• Cloudspeicher
• Datenverlust

The verb verhindern is not capitalized because it is not a noun.

This is a good question, because German usually uses articles more often than English.

In this sentence, the two nouns are being used in a very general, category-like way. That can happen, especially in headings, labels, technical language, or simplified example sentences.

But in more natural everyday German, you would often see one of these instead:

• Die Festplatte und der Cloudspeicher verhindern den Datenverlust.
  if you mean specific items

or

• Festplatten und Cloudspeicher verhindern Datenverlust.
  if you mean those things in general

So the article-less version is understandable, but it has a somewhat general or textbook-like feel.

Because the whole word Datenverlust is one noun, and the head of the compound is Verlust.

So Daten is just the first part of the compound; it does not control the grammar by itself. The whole noun behaves like der Verlust, which is singular masculine.

That is why you get:

• der Datenverlust
• den Datenverlust

not a plural form.

Yes, often you can.

German frequently allows a more general, article-less version with abstract nouns, especially in technical or general statements:

• Backups verhindern Datenverlust.
• Cloudspeicher verhindert Datenverlust.

Using den Datenverlust makes it sound more definite or more like a specific result being prevented. Both patterns are possible, depending on style and context.

So the sentence you have is fine, but Datenverlust without the article would also be common in many contexts.

Yes. German main clauses follow the verb-second rule, which means the finite verb must stay in the second position.

The basic order here is:

• Festplatte und Cloudspeicher | verhindern | den Datenverlust

You can move another element to the front, but then the verb still stays second:

• Den Datenverlust verhindern Festplatte und Cloudspeicher.

That is grammatical, but it sounds more marked or emphatic. The original order is the most neutral one.

It is a straightforward subject + verb + object sentence:

• Festplatte und Cloudspeicher = subject
• verhindern = verb
• den Datenverlust = object

So for an English speaker, the overall structure is fairly familiar. The main differences are:

• German case marking: den
• noun capitalization
• compound nouns written as one word
• verb agreement with a compound subject