Sundiro Sunray won't start
 

I recently purchased an American Sundiro Sunray ATV for my son. It started right up and ran great for 2 days. Started both using the electric start and the kick starter. I went to start it up for him today and I couldn't get it to run. It turns over but won't start. I pulled the plug and it looked fouled out to me...I cleaned it and put it back in but that made no difference. I checked the air filter and noticed there was no filter in the air box...is this typical? I feel there should be something in there. Don't know if this would cause starting problems? It just doesn't make sense to me why it would start right up one day and not the next. It sounds like it wants to start but just turns over and over. Any advice would be much appreciated.
Thanks in advance

Try a new plug, once a plug is fouled it takes more power to make it fire. Check your spark.