Depending on what you mean by "reactivate" this could be your problem:
Roku operating system version 10.5 added added a new "Power" item in the "Settings > System" menu for some of the latest Roku device models. The new "Auto power savings" item there will put your Roku device into a low power standby condition after a period of inactivity, such as when your tv has been turned off for a while.
Pressing a Roku control key on your Roku remote (not Power, Volume, or Mute keys, if you have them, which act on the TV, not the Roku) should bring the Roku out of standby and back to full operation. Pulling the power for a few seconds or a short press of the Roku's reset button should restart the Roku and restore full operation as well.
If you have a "Settings > System > Power" menu item, deactivating any power saving options you find under "Auto power savings" will prevent your Roku from going into standby in the first place.
Roku Community Streaming Expert I am not a Roku employee, only a user like you. Please, no support questions via private message -- post them publicly to the Community where others may benefit as well. If this post solves your problem please help others find this answer by clicking "Accept as Solution.".
Streaming Stick 4K+ 3821 | Streaming Stick+ 3810 | TCL Roku TV 43S245/C107X