I know how great it is to have a grill and be able to make a delicious BBQ. While you are waiting for an expert answer, I suggest you add to the thread of this question and include the full model number of your grill so that the expert can provide you with a more detailed answer. I did manage to find a link that will provide you with some troubleshooting tips. I hope my link is useful.
On a natural gas grill this problem is usually due to the burners. The burners can get grease built up on them and will prevent a good flame also I have seen spiders make webs up in the burner tubes that causes similar problems. If all of that looks good you may need to have a professional check the gas pressure to the grill.