runs three seconds and then it shuts off

I start my vehicle and it will run three seconds and shut off but I went out Saturday and it started and ran until I shut it off now it is doing same thing start it and it shuts off after three seconds I have been told it was the key the chip in the key the ignition the computer, fuel pump security module. can you help me I cannot afford to buy all these parts? no check engine light comes on so I can get a reading on my hand held computer but there is a light in the top right hand corner with a key in it and a line through it I have been working at it and it is not safety inspected yet so I cannot even take it to dealer unless I tow it there and back-would cost a fortune. thank you.