I'm sorry to hear that, and there is no _one-shot" mode of failure for the power board- they can act up for a period of weeks before failing, or just simply go out (shorted IC or capacitor, etc. will simply die without warning). If the symptoms are the same, then unfortunately the Power Supply Board in the set has failed (the most common failure with these sets) and needs to be replaced. If you, or someone you know is a DIY type and can remove the back of the TV, the board itself is "plug and play" (meaning no soldering or special tools are needed to replace it) and can be located at the link below for your set for just over $50:
Alternatively, if this is not something you're comfortable with, a shop will typically charge close to $250 parts and labor for this repair, which is on the cusp of being more cost effective to replace versus repairing it (a brand new 40" LED TV can be purchased for around $275 these days). However if you'd like to inquire about repairs, or seek a 2nd opinion, you can use the link below to locate a shop in your area if you'd like:
Other than that, I'm sorry for the bad news and wish there were a quick fix.
If you need further assistance let me know. Also, please do click a 3-5 STAR rating for my efforts before you go. That is how I am credited for my efforts by the site. You can follow up any time as needed at no additional cost.