L'ordinateur marche bien maintenant.

Because le becomes l' before a vowel sound. Since ordinateur begins with o, French contracts le ordinateur to l'ordinateur.

This is very common:

• le ami → l'ami
• le hôtel → l'hôtel

So l'ordinateur still means the computer. The noun is still masculine; the article just changes form for pronunciation.

In French, every noun has a grammatical gender, and ordinateur is masculine, so it takes le or l'.

There is not always a logical reason that helps English speakers, so often you simply have to learn the noun together with its article:

• un ordinateur
• l'ordinateur

A good habit is to memorize French nouns with un/une or le/la.

Yes, marcher often means to walk, but it also has another very common meaning: to work / to function.

So with machines, devices, or systems, marcher can mean to operate properly:

• Mon téléphone marche. = My phone works.
• La télévision ne marche pas. = The TV doesn’t work.

In this sentence, L'ordinateur marche bien maintenant, marche means is working well or is functioning well, not is walking.

Yes. Fonctionner also means to function / to work, and it is often a little more neutral or formal than marcher.

So these are both natural:

• L'ordinateur marche bien maintenant.
• L'ordinateur fonctionne bien maintenant.

For everyday speech, marcher is extremely common.

Because the subject is l'ordinateur, which is singular and third person: the computer.

The verb marcher in the present tense goes like this:

• je marche
• tu marches
• il / elle / on marche
• nous marchons
• vous marchez
• ils / elles marchent

Since l'ordinateur = it, the correct form is marche.

It is the present tense: marche = works / is working, depending on context.

French often uses the simple present where English might use either:

• The computer works well now
• The computer is working well now

Both can match L'ordinateur marche bien maintenant, depending on the situation.

In French, adverbs like bien often come after the conjugated verb.

So:

• Il parle bien. = He speaks well.
• Ça marche bien. = It works well.

In this sentence:

• marche = works
• bien = well

So marche bien means works well.

Maintenant means now.

It tells you that the situation is different from before. So the sentence suggests something like:

• before, the computer was not working well
• now, it is working well

That is why maintenant is very natural here.

French often places time words like maintenant in a flexible position, but putting it at the end is very natural.

So these are possible:

• L'ordinateur marche bien maintenant.
• Maintenant, l'ordinateur marche bien.

The version with maintenant at the end sounds very normal and often feels slightly more conversational in a sentence like this.

A simple approximate pronunciation for an English speaker is:

lor-dee-na-tur marsh byan man-teuh-non

A few important points:

• L'ordinateur: the r sounds are French r, not English r
• marche: sounds like marsh
• bien: sounds roughly like byan, with a nasal vowel
• maintenant: the last part is nasal; the final t is not pronounced

The exact French pronunciation is smoother than the English approximation, but this can help you get started.

Usually, no important liaison is made here.

You would normally hear:

• l'ordinateur as one smooth unit
• then marche
• then bien
• then maintenant

You generally would not make a liaison between:

• ordinateur and marche
• marche and bien
• bien and maintenant

So the words are mostly pronounced separately, apart from the natural contraction in l'ordinateur.

Yes. Marche bien often means not only it works, but it works properly / it’s running well.

So:

• L'ordinateur marche. = The computer works.
• L'ordinateur marche bien. = The computer works well.

The word bien adds the idea that it is functioning satisfactorily, not just barely turning on.

Yes, absolutely. It sounds natural and common.

A French speaker might say it after fixing a problem, restarting the device, or installing something:

• Avant, il y avait un problème, mais l'ordinateur marche bien maintenant.

It is a very normal everyday sentence.