How old is it? Did you buy at Walmart? This type of issue can have several causes. The back light lamp(s) could have burned out, the power supply section that powers the lamps could have failed, circuit capacitors have failed (not uncommon). Usually repairs are not cost effective unless they are very minor. Walmart advertises a 50" with roku stick ($50 value) for under $400 (http
/www.walmart.com/ip/SCEPTRE-X505BV-FMDR-50-LED-Class-w-Roku-Streaming-Stick/33563948). You would need to either haul the TV to a service location or go for in home and you would pay $60-$120 per hour for a service tech plus parts. So you can sort of figure if it is worth repairing even if it can be repaired. Also repairs usually are replacements of entire boards and circuit modules. No one does discrete part removals and replacements. Even if it is just a blown cap. you will pay for an entire new board. Lastly if you have a DLP type TV not a LCD or LED it may very well just need a new bulb and these are user replaceable.