I have a Duralast 750 jump starter. When I press the display button nothing lights up (I would check it weekly & last time was 80%). I figured it needed recharging but when I plugged it in the indicator light flashes FL% which would indicate a full charge. But, when I unplug it from wall outlet and press the display button again nothing lights up! What is wrong?

Starters tend to fail intermittently. Yes, if it started after a "whack", I woul suggest replacing your starter. Make sure all connections are tight and of course clean terminals and cables.

Yes that would be correct.

I'd suggest checking your user manual. If you don't have one, you can download one from the duralast site.

the jump start device may be low , try jumping from another vehicle with the engine running

You already have a bigger problem. The internal battery won't hold a charge. Time to replace it.

There is a battery inside which may need to be replaced. To check, run the compressor (it runs off
the battery) - if the compressor dies quickly, then the battery has failed to charge and would
need to be replaced. You may want to check your Warranty Management software (or
shoebox) to see if your Starter/Air Compressor is still under warranty - if so, replace it.
Duralast products are carried exclusively by AutoZone, Inc.
The Duralast web site: www.duralastparts.com is useless - it only shows automotive parts,
and I cannot find the product at www.autozone.com, so it seems that AutoZone fails to support this
product with replacement batteries or other replacement parts (or even an online Users manual).

I had the same problem today and I found out that is the battery itself causing the problem. It's actually the connection. So disconnect the battery and scratch the battery pins and connect them again. If you can dip them in soda water (no sugar in it!) that would be better.
This problem starts as the battery beggins to get old and combined with cold weather outside becaomes a receipe for disaster. Anyway, if you can't afford a new battery at the moment remove your battery from your car (but first try and drain it totally...leave a light on or something) and recharge it (fully) with the duralast (havbe the duralst plugget into a outlet). It will have your battery working for couple of weeks.

check you have power going to your starter motor, use a test lamp, or a multi meter, test if it lights up, when you press the starter

Think that you accidentally pressed the DISP or DISPLAY button on the back of your camera. This manually turns the LCD display on and off to save batteries. You would then use the optical viewfinder in its place. To turn the screen back on, just press the DISP button one more time.