I have a 46 inch Samsung plasma HP R4252 picture went black

Probably the power supply that drives the video has gone bad. Samsung recommends the TV go to a service center. If you have some skill and are willing to try, open up the back of the TV, remove the shielding and look at the boards to identify any obvious damage. Leaking or bulging capacitors, soot, scorch marks are the obvious. (Other parts can have bad solder or tiny cracks that are hard to spot.)

http://www.shopjimmy.com/catalogsearch/result/index/q/HP-R4252 has reclaimed parts for this TV. These are parts from TVs that were damaged in shipping and were only run during quality control tests. They list several power supplies for the model so check what part number is actually installed (there is usually a label on the board).

I hope this helps.