Ln40a550p3fxza it will not turn on

After a main digital board replacement, a firmware update might be necessary to most of the main boards.
http://electronicshelponline.blogspot.com/

The first thing you need to do is go into the settngs menu and see if you need to enable it, if there is no such menu setting, you need to change a board on the unit or use the repair kit if you are good at soldering http://www.shopjimmy.com/samsung-bn94-02077c-main-board-component-repair-kit-for-ln40a550p3fxza.htm

http://www.shopjimmy.com/samsung-bn94-01628t-main-board-component-repair-kit-for-ln40a550p3fxza.htm

CFL light should be replace

These blinks [flashes] are fault indication (Error Codes). From the number of blinks occur at one time switch ON, you can get an idea about the faulty circuit section inside it. This will make repair easy. These are called blinking codes. Make sure about the exact number of blinking of the standby/power LED, by switching On & OFF the set, for at least two times. Count it carefully. If you wish to get some details, check the site linked here. It has details about blinking codes, and fault locating procedure, to many popular brand TVs and other devices. Viewing it in "Mosaic" or "Magazine" will make surf easy.
http://electronicshelponline.blogspot.com/
Blinking codes details to many popular brand TVs are given. Surf the site with patience. If the blinks are continious non-stop; the main board to the TV is faulty.

This is classic sigh for defective power supply.
If you know how to solder,then replace all capacitors on power supply board.

I believe the correct model number is LN40A550. If so here is
the download firmware page for it..
http://www.samsung.com/us/support/owners/product/LN40A550P3FXZA

check for power supply board malfunction, replaced first bulged electrolytic capacitor. just let me know if it works.

There is a repair service for this T-Con board at coppelltvrepair.com: http://www.coppelltvrepair.com/p/539/repair-service-for-auo-t400hw01-v4-40to2-c02-40t02-c02-lcd-timing-controller-t-con-causing-bad-tv-picture

Do a google search with the model number and the words service manual. There are a lot of companies selling them on the web. It shouldn't cost you more than ten dollars