Oldsmobile/Buick Repair: engine wont start, cables, possibilities

Question
ocanionaly engine won't turn over and leaves me    stranded. maybe 20 min. later it starts ok and runs fine. repited problem. what could be the problem?

Answer
hi d. well if eng will not crank there is only a cpl possibilities.let,s start by makeing sure cables to batt are clean and tight.next be sure they are tight at starter and at eng ground .the next time it does this tap on starter while an assistant tries to crank it if starts replace starter.hope this helps  don,t forget to rate me   billy mac