1st Crash!!!

[sphelps]

I would start by testing temperature and salinity although temperature at this point may not be accurate. So all fish dead? Coral still alive? Could be oxygen. What we need is details regarding your setup:
Tank size
Equipment
livestock
what you know so far for parameters
All that fun stuff.

Equipment failure or negligence is usually the cause if such an incident. The key here would be to figure out what happened, fix it and learn from it so it doesn't happen again not just starting over.