not good和no good之別

(1) not good指「不好」，例如：
The idea is not good.
此想法不好。
(2) no good指「沒用」，例如：
The idea is no good.
此想法無用。
(3) no good又指「不擅長」，例如：
I'm no good with tax return.
我不善於填寫稅表。

（陸谷孫《英漢大詞典》）

(4) 至於no good中的good，應為名詞，類似於no use中的use，例如：

It's no good trying again.
再嘗試也沒用。
(5) It's no good可改為It isn't much good，語氣較緩和，例如：

It isn't much good trying again.
再嘗試也沒多大用處。
(6) 另外，It's no good trying again＝There is no good in trying again.