quick answer from a newbie:
>all I know is it isn't lighting up anymore when I connect ground and 5V cable
When you say "lighting up", do you mean you had the backlight working before with the connections you describe? Or simply that characters or gray or black squares were appearing?
If previously you had character blocks appearing, and its those
that have now disappeared, it's possible that nothing's wrong with your LCD, and that you just need to adjust the contrast (V0) going in to pin 3.
The LCD tutorial shows you how to do that:http://www.arduino.cc/en/Tutorial/LCDLibrary
If instead you're saying you just got the backlight
to work, then perhaps you've mistaken pins 15 and 16 for pins 1 and 2. According to the datasheet you referenced, the backlight comes on if you supply +4.2v across pins 15 and 16 (with 15 gnd and 16 +4.2v). These 2 pins are at the other end of the module from pins 1 and 2. If you did
mistake the two sets of pins then your described wiring would have wired the backlight with inverted polarity. I don't know if that'd damage the backlight or whether it's protected on that module.
Hmm, I've re-read the datasheet and the "features" section suggests that the backlight can also be driven from pins 1 and 2, though the pin connections section doesn't. I'll leave my original thinking about the backlight wiring intact for now, but please take it with a (further) pinch of salt.
Tell us how much you had working before, and describe all your connections to the LCD.
p.s. You don't normally have to wire up the backlight to get the LCD working.