This sentence doesn't look correct to me...

It's totally wrong and doesn't make sense. Someone will have to check the Japanese. When I put it through the google translator it comes up "The room got cold".

I'd argue that the English is partially wrong (one extra letter and punctuation mark), and points toward an intended meaning: "It froze hard last night". "It" refers to the weather, and "froze hard" means that the temperature dropped significantly below the freezing point of water, such that small puddles of water will be frozen into hard pools of ice, and sensitive plants will die.

While I think I get the meaning, I am used to a more passive way of expressing it: "We had a hard freeze last night." I don't know that I've ever heard the concept expressed in the way the current sentence does. It's certainly worth checking the Japanese, as Dejo suggests.

Kono heya wa hidoku samui
according to my japanese dictionary means
this room (is) cruelly, harshly cold

So in the japanese sentence there is
- no mention of last night
- mention of the room

So the English sentence, in addition to it's structural flaw, has a meaning which appears to have little in common with the Japanese. How can we correct this problem.

Well, we'll wait until someone can confirm the (seemingly correct) interpretation of Hans and translate the sentence into good English. Maybe "This room is harshly cold."
Anyone who thinks he got the meaning of the Japanese sentence can adopt the English one and change it, as there's no owner.

It's been corrected by Jesse.

The Japanese means the room is cold (with an intensifier - very, awfully, extremely, ...).

...five years later...
I adopted it and changed it to what I believe is the correct translation of the Japanese, which is in line with the comments above. The only other translations are indirect ones from the Japanese, and they appear to be correct already.