Do the best you can to keep it warm and hydrated, and give it some time. Since it's made it 48 hours, I wouldn't give up just yet, but would be prepared to accept that it may not make it. Sometimes they just need encouragement to want to live. But as stated before, there is always the possibility that there is an underlying problem. I've nursed weak chicks that didn't make it, some that went on to live full, normal lives, some have succumbed at a later date to issues that were probably the reason they were weak as chicks, it's hard to know when they are so small, but I always try to give them a chance. At any point if you think it's suffering, it's perfectly acceptable to euthanize, that is a call that only you can make.