Hello & Welcome to JA,
Check the fuses in the under hood electrical center. I have seen several that blow the FICM (fuel injection control module) fuse.
The 6.6 Duramax only uses a fuel pump if there are 2 tanks & this is used to balance the fuel in the aux. tank. The fuel injection pump uses vacuum to draw the fuel out of the tank. Go to the fuel filter under the hood & push the prime bulb about 10-15 times & then try & start .If it starts you have lost vacuum in the fuel line or have an air leak.
If the fuel system will not even briefly prime to 10 psi and will not start, the check valve in the fuel filter/heater element housing is stuck open.
Ok,press the bulb about 10 -15 times & open the bleeder to see if any air comes out. Press the bulb again about 10-15 times & see if the vehicle will start.
If air comes out ,there is an air leak in the fuel system,if you have not recently had it open.