Starter not working?

I have a 2000 Malibu LS. When I try to crank it; it turned really slow then started. But after sitting for a couple hours now it just clicks once and doesn't start at all.
This has happend in the past while I was driving the car would turn off and the steering will tighten up, I had to pull on the side of the road, which was very dangerous, my mechanic Got the car towed to him, and he said it started right up, he put more gas in it and drove it around on and off for 4 hours. The 2nd time it turned off I waited a couple hours when I tried starting it, nothin, no click sound or turn, all lights and radio comes on, it's not the battery, tried to get a jump. So we figure something wrong with the gas hand and maybe I should keep the gas above the half way line.
(so back to what I was saying @ the beginning)
Last night I go out for a bit the car is running just fine, then out of no where I try to start it and it turns really slow, I turn off then try again and it starts, I go to a friend of mine house, cut the car off and it does the same, so this morning same thing happens, and couple hours later, now it only clicks once when I try starting it. Thought it could be fuel pump but got that checked, good battery, I don't know if it could be the alternator or starter. Any suggestions?