The power button on the TV doesn't work because of the child lock?
I went over the copy of your manual for your TV. It must be the child lock timer problem.
I would try leaving the TV unplugged for 30 mins and see if that reset the TV and releases the lock.
If it doesn't work, the remote needs to be replaced. A universal remotes aren't really universal when you need to use special buttons. The remote made for the TV is the best.
If your TV is the model 47PFL7403D, here's the cheapest place to buy a replacement.