What do you do when you can not solve basic things?
I'll give two bits of advice. Both may be hard to do. The first is to relax. Some things in mathematics are just very difficult. The experiences you have had with the material itself seem completely normal to me. 

But the second is to try to find a more compatible and helpful advisor. Your advisor may not be bad, but seems ill suited to help you with what you need. 

I can't judge your math background, of course, but if you can pass graduate courses it must be ok at least. Maybe excellent. 

Your inability to solve basic problems may be overstated. It may just be "brain freeze" based on your emotional state. It may be that you are better suited for longer reflection rather than quick answers. But, until you learn to relax you may continue to have problems. Many people use periodic physical exercise to help them relax and give their mind a rest from work. But perhaps you need something. You might even need to talk to a counsellor. 

I think my own advisor was helpful, but day-to-day I worked on my own. He gave me problems to work on. The first was too easy, so no real challenge. The second was too hard, so no progress. The third was just right, though it still took a year to but the thesis together. I was lucky in a sense that I went through my low period before I met him and so had bounced back and was able to be more productive. But a low period is pretty normal for math doctoral students.