Will not start

I have a 2001 Audi a6 2.8 Quattro that will crank, but will not start. Tried jumping. Recently changed the starter and ignition switch. Fuel pump has power at pump, but is not activating when I turn the key. Power windows, roof, and AC/heater are not working, and when I turn the key, the gauges do not move accordingly. Do you think it is just the fuel pump or some sort of electrical or fuse/relay issue?

Earlier in the day the car would not turnover, but did with a second attempt and drove home with no problem.

Previously the car had occasionally periodically turned over on ignition, then immediately shut off, but would fire back up and run and drive as expected.

Please help!

Turns out it was the ignition switch, again. Thanks for the advice though, much appreciated.

2000 Audi A6 six cylinder all wheel drive automatic 139,000 miles.

My car will not start after running, but if it sits for a few hours will start just fine. Please help!

It cranks very good it is not a battery issue. But when it has seat for a few hours it seems to start just fine, you can smell a lot of fuel though. Please help.

Every morning the car is crank about five to seven seconds before start.
Just happened a couple days ago, the morning my car start normal, I drove it a couple feet, than the engine stop. I try to start again, but will not start.
Checked the gas, was a little low, but about quarter of tank.
About ten minutes later the car just start, and run all day, but after that happened the same crank problem is keep coming back every morning, and when I stop more than twenty minutes.I was ask my Audi mechanic, he checked test the car, no system errors, no check engine light, nothing. He said have to change the fuel pump. I am not sure because the car runs, so the fuel pump is functional all time. I was checked myself the tank cap gasket have a little bit a crack on it, so could be a little leak, what cause the problem? The other idea was put some Techron in to the fuel to clean the system and injectors, what seems to be good the car running smother but did not fix the problem.
I hope you get enough info to help me out.
Thanks

Thanks

Do you think I can just check the check valve with out change the fuel pump?
Because that was the first quess, the check valve, after start the car runs.

After a time running my car I turn off the engine and later when I try to turn on the car didn't start. Then I waited for a minutes tried again and the car started.

Cranks over but does not start. I used the scanner to check the car and the scanner found problems with the camshaft position sensor. I already change it and the problem is still hanging around. Somebody told me to change the crankshaft sensor.

Hi there, I have an Audi A6 that will not start I am 98% sure it is because of the starter because it is an manual and I push start it. But when I get it started if I do not give it a lot of gas it turns back off. Going around a corner or when stopping it turns off.

The reason I think it is partly because of the starter is that when I turn the key it does not crank the motor at all I do not hear any noise either. But what could be the reason for the whole car shaking crazy?

How can I tell if the power is getting to the starter? What is that I am suppose to look for?