Laptop screen black/wont boot up.....HELP?

I have a Dell inspiron 1721 running windows 7. when i turn it on i can hear the hard drive start up and the fan start but there's nothing on the screen! If i take out the battery and plug it out of it's charger and hold the power on for a minute then plug it back in the num lock and caps lock leds start blinking. Also i got the battery i have about 3 months ago as a replacement and i got a replacement charger about a year ago. I've had this laptop for around 3 years. Oh and also if i dont have in the battery but have it plugged in to the charger the fan doesn't start. PLEASE HELP thanks ;)