My crown fell out and the tooth underneath is broken. What is the best option?

It is best to see a dentist to have xrays taken and have clinical examination done. You might be needing a root canal, a post and another new crown made. If decay caused the problem and and the decay is extended to the root or bone, then you might need surgical intervention!see an expert dentist right away.

Hi:You might need a root canal and a post to save the tooth if the fracture is not too deep.  Otherwise you might need a extraction and implant.Best,Dr. Maddahi

There’s just no way to know if that tooth can even be fixed without seeing a dentist for an exam and x-ray. That tooth broke for a reason, it could be decay that was hidden under the crown, or something else. An x-ray is the only way to see below the gum and a dentist appointment is the only way to know what your options really are.

Very sorry to hear that you are having trouble with your tooth. It sounds like part of the tooth has broken beyond the crown part and a dentist will need to fix it for you. The least expensive option would be to find a dentist with a good reputation who offers an in-house discount plan. Many dentists are starting to help non-insured patients with low-cost, preventative oriented dental plans that provide discounts on procedures like crowns. 

Hi! Thanks for your question. I recommend go to see your dentist as soon as possible and do not try to cement the crown on your own.
Good Luck.  

Your best option would be to go and see your dentist as soon as possible to prevent any further damage. Temporary over the counter solutions may cause more damage that will take much more work (and money) for your dentist to correct. Please make sure to see a dentist as soon as possible! 

Thank you for your question. I have to start by saying that unfortunately, usually, when you can not get your crown reseated it is because either the crown itself has broken slightly or part of your tooth has come away. Your best option is to see a dentist as soon as possible and avoid using any shop purchased temporary cements as these will make it harder for your dentist to refit the crown if it is possible. Hope this helps Kind regardsThomas Dey, BDS, MSc

Hello!
Well, if its just the crown that is broken, but the root still has a good structure left, its possible that you can get a root canal and a post so a new crown can be placed, of course to verify if this is possible xrays need to be taken by your dentist. 
Hope this helps, good luck