think of 是想起来,think about 是想一想
或者这么说,
想起来是突然终于想起来某件事某个答案了；
而想一想,是说想一想这件事分析一下这件事（这个问题,这句话）.
可以根据汉语的意思来理解
你好好想一想这个问题,就会想起来一个解决办法.
please think about the question,you will think of a solution.
如果说“想一想这句话什么意思” please think about this sentence,you will see what it means.
我终于想起来那天下午我做了什么了.I finally think of what I did that afternoon.