As Dan stated, we need more detailed info to help.
When you say no hot water flow...do you mean no water flow at all when the hot water is turned on...or do you mean that the water just isn't hot that flows out the tap?
If the water just isn't hot, but does flow out...it's probably the bypass valves set still for winter mode...like Joel said. The Sasks have a great pdf file that you can download that shows how the bypass valves are set for winterization. If you still have the bypass valve(s) set in winterization mode, then you are mixing cold water into the hot water.
Request for Winterization & De-winterization Instructions
The white crud that came out could be the pieces of your sacrificial anode rod if you have a Suburban brand water heater. A piece of this could also clog up stuff.
Anode facts and FAQs
Drain the hot water heater?