Reduce current in momentary latch toggle / source capacitors
Your only fault was not knowing the Vss range for the 74HCxx family is 2 to 6V above which the CMOS goes into excessive cross-conduction mode failure.

Here is a link to see how prefix affects Supply voltage range options. 

Here is a link to see various ways of making a momentary switch toggle an output.
Here are a bunch more with some irrelevant images. 

A 2 input NAND with inputs shorted together is just an inverter.



Generally it's a bad idea to leave CMOS inputs floating so unused inputs are usually tied to 0 or V+. (ESD issue) Each part number has a datasheet. Never assume until you have them memorized. The oldest was CD4xxx then 74HCxxx then 74AHCxxx etc each going to different supply ranges and speeds.