Please turn off the power.
请把电源关掉。

======================================

Turn on 跟 turn off 算是最常见到把电源打开和把电源关上的字眼了。例如你可以说 "Could you help me turn on the microwave?" (能不能帮我打开微波炉？) 或是 "Please turn off the power before you leave." (请在离开前把电源关掉。 ) Turn on 和 turn off 是一对很好用的片语，务必熟记。
但是如果今天换成另一种情况，我想说：「不要关掉，让它一直开著。」这句话要怎么讲呢？很简单，你可以说 leave the power on 或是再偷懒一点说 leave it on。比方你回家前可以交代同事， "Just leave the printer on when you leave." (你们走的时候不要关掉印表机，让它一直开著好了。)

Please turn off the power.
Could you help me turn on the microwave?
Just leave the printer on when you leave .

Could you help me turn on the compter?
leave it on!!

A:Can I use your computer ?

B:Certainly ,but please turn off the power  before you leave .

A:OK ! I'll do it !