My Lexus sc300 keep not startinh3

Hey I really need help. I have a Lexus SC300. Its my
joy ride car. So I don't drive it much. Like out of a
month maybe once but that's every few months
tho. Cause I work 5 to 7 times a week all day. But it
be moved once a week for street sweeping. I am
the one that give it 5 to 8 mins every time I start it
up before I drive off. I also keep the gas on full. But
I been working so much im not home to move it so
someone do it for me. But 3 weeks ago, I go to get
in the car for a nice ride and it want start.
...So I check the gas and its
on E. So I went to the gas station got gas, enough
to drive to get a full tank..(Hold up 1st it was a full
tank when I last was in it. So the man said the gas
evaporated.(I dont know if that's true but
something happened.) 2nd my car is on a slight
hill.) I came home a little after went to get in it it
didnt start. I sent it to the shop. Changed the water
pump and a turn up. I went to pick it up and drive
home and parked it. Went the next day to drive it
and it didnt start. I sent it back. Now he called me
on Wednesday to come pick it up, today just now i
went to start it and it didnt start. These is crazy I
leave him it start I get home and try it. It want start.
I have a new battery and its sounding like it want to
start but it want..PLEASE PLEASE PLEASE HELP
ME!!!!