key turns on but wont crank on 1998 Infiniti I30

my battery was dead i jump started made it to work ,after work dead again put a new battery in worked fine for 5 days now key turns all ind. lights come on but car wont crank all lights head lights are brite .but it wont crank even with a jump start

3 answers
first make sure u have 12v on battery by itself , , then clean cables terminals very well ,, connect back and inspect alternator , it has to generate at least 14v ....
Have starter checked
have charging system ck and also ck starter