No-one could use the computer unless they had a password.是什么意思？

No-one could use the computer unless they had a password.

除非知道密码，否则谁也用不了那台计算机。

could

aux. “can”的过去式，能够，打算，用于假设语气的条件句，用于虚拟语气的结论句；

例句
The regulations were relaxed and the prisoners could get out and about a bit.
规定有所放宽，犯人可以出去短暂放风。

use

n. 使用，使用权，功能；

例句
Abstain from sex or use condoms...
禁绝性事或使用安全套。

the

art. 指已提到的人（物），指说话人与听者已知的人（物），用于独一无二的事物前，与形容词最高级和序数词连用；

例句
He did have a real knowledge of the country...
他对该国的确知之甚多。

computer

n. （电子）计算机，电脑；

例句
The image is then stored on the computer hard disk as a vast array of black or white dots.
这幅图像当时就以大量黑点或白点排列的形式被存入电脑硬盘。

unless

conj. 除非，如果不；prep. 除了，…除外；

例句
No-one can set up a waste disposal company unless they can show that they've got enough money and trained staff to do the job properly...
任何人若想成立废品处理公司,必须证明其拥有足够资金和受训员工以保证工作可以顺利开展。

they

pron. 他/她/它们，人们，大家，政府，当局，她们；

例句
The storms had abated by the time they rounded Cape Horn.
他们绕过合恩角时，暴风雨已经减弱。

had

v. 有（ have的过去式和过去分词 ），（亲属关系中）接受，拿，买到；

例句
He claimed that his parents had abandoned him...
他声称父母遗弃了他。

password

n. （进入房间、建筑或某个地区的）口令，<计>（使用计算机操作系统的）密码；

例句
Castanet's next version promises additional security, with password access and encryption.
下一版本的Castanet将通过口令访问和加密增加安全性.