No picture or sound

SOURCE: monitor only stays on for 3 seconds

There is probably a bad capacitor within the monitor that will not allow the picture to "hold" in the on configuration. This will need to be replaced. You can send it back to Phillips, or 17" monitors are pretty cheap these days. I would suggest a Samsung or BenQ. They both carry 3yr warranties.

SOURCE: The screen its totaly black

Right, Following is part number of required flexible wire..
" 1-864-761-11 " --FP-185 FLEXIBLE BOARD
It is available in Part Store for $26
Qualified tech will charge approx $100 to fix this camcorder.
Good luck.

SOURCE: sharp model lc19sb25u sound and no picture screen

Part called main unit failed and require replacement. part number duntke352fm02.

SOURCE: screen is black

Try connecting it to a external monitor and see if it comes on. If now then most likely due to a faulty GPU. Check out www.bootmylaptop.com for a DIY repair guide.

SOURCE: Have a RCA flatscreen model # L40FHD41, blue power light comes on and stays solid but I don't get any picture or sound. Screen stays completely black as if it doesn't have any power at all.

Other than checking all the connections going to it for signal it is likely a shop repair.

The nature of these sets is someone must open and inspect them and check for voltages missing.

At that point it becomes a guessing game---try the boards (purchase them) and see if a bad board.

It is always possible the front screen unit or display has failed which is fatal cost wise.

You have to weigh the cost of repair, age of set and cost of replacement in this.

The only way anyone can KNOW which board is bad is to actually remove and replace it----most shops look at it and shoot you a high estimate.

let me know if you have questions.