My blackjack's keys wont work
First off, how do you know it's the keys, rather than something else? More details are always helpful. An important question is, can you see or hear anything at all, by any means? If someone calls you, does the screen light up?
If you see incoming calls, but can't answer them because the keys don't do anything, then I'd ask if the phone might have the keyboard locked. You'll be able to tell because you'll see "Unlock" in the lower left of the screen when someone calls or you press the power button (top left edge, above the screen). If it's locked, pressing the "..." button to the left of the wheel will tell you how to unlock it (just the "*" button down by the "0" button on my Blackjack).
If you don't see anything when someone calls, you might want to figure out if the phone is working at all.
A couple of ideas (sorry if any of these seem obvious - it's bad form to miss simple solutions):
1. Is the phone powered on? You can turn it on by holding down the power button (top left edge, above the screen) for several seconds. If you make it to 10 without the phone coming on, then it might be the screen, the battery, or the phone itself.
2. Is the battery dead? Try plugging the phone in and then holding down the power button, as above. If it still won't work, try removing the battery, then plugging it in and doing the same thing over again. When you plug the charger in, you should see a Duracell-like image on the screen, even if the phone is turned off. If you still don't get any sounds or anything on the screen, it sounds like the phone has serious trouble - probably needs professional help.
3. If you hear sounds ("swooshing" on mine) when you turn it on or off and the keyboard lights up, but don't see anything on the screen, it sounds like the screen might be bad - probably needs professional help.
4. Finally, you could try connecting it to your computer with the sync cable. I haven't done that with mine, so you'll have to read the instructioins, but it might let you know that the phone is working internally, but having communications problems through the keyboard and/or screen. If that's the case, you can try fixing it yourself or get an estimate from a professional. Good luck!