My car is sometimes starting and sometimes not.

My car is sometimes starting and sometimes not, I have had it in the shop for the last two weeks and it has started fine every time they have went to start it, but then I get it back because they don't think anything is wrong and it won't start for me. Sometimes when it isn't starting, it will start just fine the next day. When I turn the key and it doesn't start all the lights and radio comes on, the engine just doesn't. I read previous comments about putting it in neutral and trying to start it after that so I did that and that didn't work either. Is there any other explanation for this? I try not to even drive it anymore in fear of being stranded somewhere and it is getting really frustrating.