It's not clear what the ciscumstances are.
However, I give it a try.
Maybe you just got this phone, installed it by hooking up the power. In such case you should carefulle have read the manual.
Did you connect the poweradapter ?
A) Some phones require a cable-connection (RJ45 connector), either to another phone-station or straight to the land-line inside your house / office. Check this connection if you made this cable-connection.
B) Some DECT-type, and require another (wireless) station to be connected to (wireless). Check the manual how to connect your phone to this remote, wireless station.
In some cases you might face some hardware / technical problems.
If there's no light at the display, you got probably a battery-problem. If you own this device already for a long time, you might have a fair chance the battery is old and should be replaced.
If the phone is new, you should check the power-adapter which is charging the phone (it's batteries).
Check if it is connected well to the power-outlet. Some adapters contain a built-in small LED (light), which will emit light when connected to the wall-outlet. When plugged in correctly, the LED should emit light (red or green).
B) No contact
The module, or also called "station" is the part where the phone slides in, when you're not using your phone. However, it's possible the connection from the adapter to the phone is not perfect.
The other end of the poweradapter should be plugged correctly into the module/holder.
The module / station contain some (gold-alike) pins. The phone, contains gold alike pads, which should connect to these pins, when the phone is located in the module.
Sometimes, due to malfunction in manufacturing-, or even logistic process, the pins might get mis-aligned. Or, even rough (ab)use of sliding the phone back into the station might result in mis-alignment of these pins. In such case you can (carefully!) re-align these pins.
I hope you could locate your problem and solve it by this message.