Getting really depressed about school, work, and life?

I'm in a really hard graduate-level computer science course where groups of 3 work on homework together. I understand what the homework questions are asking, and I know the general approach I need to take, but I can't think of specific answers. I've spent several hours trying to solve these problems, but I can't solve a single one. The answers just seem to come naturally to the other two in my homework group. I feel really bad because we are meeting tomorrow to discuss the last few problems of the homework, but I haven't contributed anything at all to the solutions. I'm even having trouble understanding *their* solutions! I hate this feeling, and it makes me worry about how I'll do on exams.

This is my last semester before I graduate. I want a job in a completely different (already selected) field, and I'm only completing this degree so I'll have something to fall back on. But it seems like I will have to dedicate my life to get these 4 credit hours, and with my current progress, it doesn't seem like even that will guarantee me a passing grade. I can't drop the course and pick up a different one because of certain degree requirements. I don't even want this degree, and now I'm being told that I have to be miserable for 4 months to finish it? I'm just too scared to leave in case things don't go well in my new career path.

I'm sitting here trying not to start drinking or giving up and going to sleep. I just feel so stuck. I've been taking breaks (I've been working on this homework off and on for 3 days now). I've been getting plenty of sleep. I don't know what's wrong! Please someone help me.