If the Nokia C7 shows charging indication when the battery charger is being plug-in but unable to switch on when pressing the power switch button, this solution might possibly help fix and solved the problem.
This solution shows the connection line paths of Nokia C7 Power ON OFF switch which can be used for applying jumper when the power switch is not working or unable to turns ON the device .
Nokia C7 Power ON OFF Switch Jumper Ways
The highlighted components above is where the power switch is being connected, if these components were damaged it will result to power switch failure. You may need to check and then replace these components as well.
There is a risk that the power switch on Nokia C7 may sometimes damaged and the switch terminal solder pads will be lifted and found hard enough to install it back. If these happens you may need to strongly bond the power switch to its original position and do a apply a jumper wire on it is one of the option.
You can use the solution above to determine which particular components you can put and solder a jumper wire when needed.