Well, here's my story...
I went 24 frustrating hours before I went solo. I think when I got to 14-15 hours I was getting worried and asked my instructor what I was doing wrong. He told me to persevere, I was nearly there and some time soon everything would just 'click'. Well it didn't seem to, and I was seriously considering throwing the towel in at 20 hours.
But then I had some business in the US, and found a flight school over there. I just went flying with an instructor for a couple of hours, he told me where to fly and talked on the radio. I just enjoyed the controls and flying somewhere for lunch.
I got back to the UK and a couple of hours later I was solo. In my mind the hours and hours of frustrating circuit practice getting nowhere were the problem. I'd suggest to anyone having problems, just to ask their instructor to take them "flying", fly somewhere, land away for a break. Come back refreshed and motivated.