There are several questions that you need to answer:
1) are you behind in your mortgage payment
2)are your HOA dues current. It is important that you maintain these dues no matter what
3)what are your goals, do you wish to stay in the home? If so you need to look into the making home affordable program http://www.makinghomeaffordable.gov/
or call 888-995-HOPE
If you absolutely can not afford the home any longer then you will need to contact your bank asap to begin the short sale process. Please understand that you must be able to show a hardship has occured since the last time you refinanced. Simply saying you can no longer afford the home is not enough. A hardship would be a death , change in income, job loss, disability etc. You would have to document the hardship.
The most important thing you need to do if you decide to sell is hire an EXPERIENCED short sale Realtor. Do your research and make sure that the person you use to sell you house know what they are doing. It can make or break your deal.