You should check the battery and both cables. You should also look for corrosion on the other end of the cable on the block. If you have any questions, feel free to e-mail me at Ray Brandt Nissan Answer Guys
I had a huge problem with my starting my SE-R for a long time.
Changed a few starters and nothing...
Turns out my ignition switch is bad.
I just ran and external switch through a relay and never had a starting problem again.