2001 Nissan Sentra 2.0 start up problems

I have the following problem: A couple of weeks ago, car didn't want to start. Turned of the switch, turned on, no luck. Tried it a few times and it worked, started and engine was humming, no sputtering, no stalling. Turned it off and it started again without problems. No problems until next week, when I left it warm, and after 5 min it didn't want to start. Tried it couple of times, no luck. Left it and after 12 hours tried again. Didn't want to start. Sluggishly, I managed to start with a power and jump cables from another car. I think low power is not the problem, and I will tell you why: I hear knock when ignition is on, and then no spinning of the starter. Changed the battery with a new one, didn't work out. Same problem exists, starter is knocking and no spinning. Tried with power from another car. Doesn't want to start. On a couple of time it cranked with somewhat very low power and of course it didn't want to start. It seems like the capacitor is blown, if one exists on this car.
Can you point me what to change next and give it a try? Crankshaft position sensor, mass air flow sensor, oxygen sensor, or what.