no start 6.0

[Ironwolfe]

I have change the headgaskets on a 2006 6.0 and now it will not start. It sounds like its out of time. It cranks slow and sometimes tries to lite but dosen't. Also I noticed that the oil pressure gauge goes to normal when you turn the key on, if I disconnect it, it reads zero. I have checked all the wiring connections, fuel is present at banjo fitting on the head, and there is oil in the high pressure manifold. The batteries do seem a little weak but even with a fresh charge it seem to turn slow.