Wǒ wàngjì le zhànghào de mìmǎ, suǒyǐ xiànzài bù néng dēnglù.

Here 了 marks the forgetting as a completed event: I forgot the password.

Without 了, 我忘记账号的密码 sounds less natural in this context and can feel incomplete or more like a general statement. With 了, the speaker is referring to a specific thing that happened, and that completed action explains the result that follows: so now I can’t log in.

You might be understood, but 我忘记了账号的密码 is much more natural here.

Why:

• 忘记了 = a completed forgetting event
• the sentence then continues with a consequence: 所以现在不能登录

That completed-action feeling is important. In conversation, people also often say 我忘了账号的密码, where 忘了 is a very common shorter form.

的 links a modifier to a noun. Here it works like of or ’s in English.

So:

• 账号 = account
• 密码 = password
• 账号的密码 = the account’s password / the password for the account

It shows that the password belongs to or is associated with the account.

Because the main noun here is 密码. The speaker forgot the password, not the account.

In Mandarin, the structure is usually:

modifier + 的 + main noun

So:

• 账号的密码 = the password of the account

If you said 密码的账号, it would mean something like the account of the password, which does not make sense here.

所以 means so or therefore. It introduces the result:

• 我忘记了账号的密码 = I forgot the account password
• 所以现在不能登录 = so now I can’t log in

It makes the cause-and-effect relationship very clear.

No, you do not need both.

Mandarin often uses:

• 因为 A，所以 B = because A, so B
• just 因为 A
• just 所以 B

This sentence uses only 所以, which is completely natural because the cause is already stated in the first clause.

You could also say:

因为我忘记了账号的密码，所以现在不能登录。

That is also correct.

Both are possible, but they mean slightly different things.

• 不能登录 = cannot log in / am unable to log in
  This focuses on the present inability.
• 没能登录 = was unable to log in / did not manage to log in
  This focuses more on a failed attempt in the past.

In this sentence, 现在 is present, so 现在不能登录 is the best fit: right now I can’t log in.

能 means can / be able to. To negate it, you normally use 不:

• 能登录 = can log in
• 不能登录 = cannot log in

This is the standard way to express inability in the present or general sense.

In Mandarin, time words usually come before the verb phrase.

So the structure is:

• 我 = subject
• 现在 = time
• 不能登录 = cannot log in

That gives:

我现在不能登录 = I can’t log in now

In the full sentence, 所以现在不能登录 means so now I can’t log in.

Yes, 登录 is a verb. It means to log in / sign in to a system, website, app, or account.

Examples:

• 登录账号 = log into an account
• 无法登录 = unable to log in
• 登录页面 = login page

In modern Chinese, 登录 is the standard word for digital login.

They are pronounced the same, but 登录 is the correct form for logging in to a computer system or website.

• 登录 = log in
• 登陆 originally means to land, especially coming ashore from sea or reaching land

In casual usage, some people write 登陆, but for standard written Chinese about accounts and websites, use 登录.

Sometimes, but they are not always identical.

• 账号 usually means a login account or account ID
• 账户 often means an account in a broader sense, especially a bank account or user account in a system

For logging in, 账号 is very common and natural.

So:

• 账号密码 = account and password
• 银行账户 = bank account

Yes. A very common spoken version is:

我忘了账号的密码，所以现在登不上。

Differences:

• 忘了 is a very common conversational form of 忘记了
• 登不上 means can’t log in in a more colloquial way

Another natural version is:

我把账号的密码忘了，所以现在不能登录。

All of these are natural; the original sentence is clear and correct.

Both can work.

• 忘记 is a little fuller and slightly more formal
• 忘 is shorter and very common in speech

So:

• 我忘记了账号的密码 = correct and natural
• 我忘了账号的密码 = also very natural, especially in conversation

Learners will often hear 忘了 more frequently in daily speech.

This is a useful pronunciation point.

不 is normally fourth tone: bù. But when it comes before another fourth-tone syllable, it changes to second tone.

Since 能 is second tone, there is no tone change here:

• 不 能 = bù néng

If it were before a fourth-tone syllable, then it would change:

• 不是 = bú shì

So in this sentence, say bù néng.

Yes. In many situations, native speakers may simply say 密码 if the context is clear.

For example:

• 我忘记密码了。 = I forgot the password.

But if you want to be specific, especially when there may be multiple passwords, 账号的密码 is helpful and clear.