I have a 2000 Dodge Durango 4 by 4 with the 4.7 engine is throwing the camshaft sensor code I replace the camshaft sensor replaced the crankshaft sensor and the computer and it's still won't start

May not have been a faulty sensor but a problem with the camshafts or more likely the weak timing chains in these motors. The 4.7 engine's timing chain (actually 3 chains) has two hydraulic tensioners and plastic guides, and cause a lot of issues with misfires and engine shutdowns (knock sensor). If the truck was running (even if it was poorly) prior to changing out the computer I'd check to make sure it was programmed correctly. You might have created a second issue while trying to fix the 1st one.

It won't stay at all and would not start at all before I changed out everything but was and is throwing P0340 code for camshaft sensor

The problem may not lie directly with the sensor but the wiring or along the circuit, you could test for continuity between the camshaft sensor and the PCM, but you'll need a pin diagram. Check that you have 12 volts. According to a list of causes for this code on the OBD site, it might be a bad starter too. It states the PCM doesn't read the signal from the camshaft position sensor for the first few seconds during startup so it might not be the reason your durango isn't starting. ---- http://engine-codes.com/p0340_dodge.html ----