at the end of his rope  

智窮力盡;進退維谷

explanation :  Frustrated or ready to give up.  Someone who is at the end of his or her rope has lost patience or ability to deal with a situation.  It may be a case where someone has tried many options and has run out of ideas. 

e.g. Peter tried everything he could think of to repair the truck, but nothing he does makes it run.  He's really at the end of his rope.