Car still not starting @#$#%%$

Car sounds like its not getting enough power. Battery reads 12.87 volts, I just replaced the battery terminals with new ones and made sure they were clamped down tight. Also checked the ground near the battery and the little box of wires next to the battery. But still the car sounds like its not getting enough juice...I am seriously at my wits end I need to sell this car but its not starting. Any ideas would be great thanks.