NXT screen either flickering or blank, what do I do?
Here are the two easiest options:


Replace it. Contact LEGO, and tell them of your problem. I've
hear many success stories from people who did this, and LEGO
replacing it for free. For one person, it took a week to arrive, but
for another, three days. Note that if you want to keep your old NXT,
you'll have to have the receipt. If you don't have the receipt, then
you'll have to send them your deffective NXT. Also, if you did not
buy your NXT directly from LEGO, (i.e. Ebay) they will not replace
it for free, but rather ask that you pay them to repair it.
Repair it. If you have a soldering kit, then get it out, and follow
the instructions in this video. It worked for me the first try.