I have a 2000 jeep grand Cherokee with a 4.7 v8 just put new head gaskets water pump elec fan and clutch fan also new radiator , and thermostat. About a month ago however I guess I got a bad thermostat because it didn't open the other day and my jeep overheated I had the jeep towed to my house took out the thermostat and put it in boiling water it still didn't open. So again I replaced it after that I tried for the first time after overheating to start it and it will crank just fine, but will not fire up what could be my problem?

Was the head machined? Did you check that there was no damage done to the valves? If it overheated badly the other day, the aluminum head may have warped again. Other than that, go through all of the normal stuff; e.g. checking all under hood and under dash fuses with a test light or multimeter, checking for codes, checking for spark, and checking for fuel.

I did a compresion test on all cylenders and a pressure test on the cooling system all is good there