Why is my back light not working?

My lighting is not working so I can not read my text it is to dark. I'm not able to do much because i can't really see anything

crwdns2934089:0crwdne2934089:0 crwdns2934093:0crwdne2934093:0

crwdns2934109:0crwdne2934109:0

crwdns2889612:0crwdne2889612:0 0
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