First of all, welcome to the forum
Secondly, you have posted two threads asking the same question - so I have deleted one of them. Please try to only post once for each question you have. Thank you.
To begin with, let's clarify that the tablet is, in fact, charged. Please check that the charger is correctly assembled and that all the parts are clipped together well. Probably best to disassemble it & then reassemble it. Then plug it into a different outlet and see if the tablet powers on when the outlet is turned on.
If the situation is that the MeMo is charged, then here are a couple of things to try...
1) As the tablet is off, start with a cold boot (see link in signture) - or
2) Try a loooooooong press on the power button - hold it down for up to 60 seconds
Let us know how you get on.