Starting problem

I went out to my car this evening to defrost it as was covered in snow. my car started no problem and was running for about 10 mins and when i was done i turned the car off. i went back out to it about 20 mins later and i went to start it and nothing happened it did not even turn over no sound what so ever.i have tested the battery and its fine but short of that i am stuck if any one could help i would be very greatful many thanks