try removing the battery pole clamps and re-attach them (minsan kasi kahit mahigpit ang battery poles eh hindi dumadaloy ng maayos ang current)

... if still no avail, possible your battery is nearing its life span and needs replacement,

last possible cause is the starter itself, it may need to change its carbon contacts or the solenoid, but replace the carbon brush first prior changing the solenoid... the solenoid also depends from the carbon brush..