Sounds like you have the system in partial bypass mode for winterizing. And the valve on the hot water line is closed along with the bypass valve.
When "summerizing" the bypass should be closed and the hot and cold should be open.
Is " summerizing" a word?
Did you have water in the water heater? Did you light the water heater?
If you can't get hot water. It may mean that the water heater was not full. If you fired it up empty. It may have been damaged. So check for leaks.
Knowledge: "A gift to be shared. A treasure to receive."