rack one's brains to try very hard to think of something 绞尽脑汁,苦思冥想

I've been racking my brains all day trying to remember his name.
我一整天都绞尽脑汁,想要回忆起他的名字.

sidetrack:to make somebody start to talk about or do something that is different from the main thing that they are supposed to be talking about or doing 使转变话题;使转移目标

I was supposed to be writing a letter but I'm afraid I got sidetracked. 我本来应该在写信,但后来恐怕是分心干别的去了.