If unplugged the device for a long time, will there be any affect to the device?

After unplugging and replugging the device. The Set Top box will automatically self-check before resuming work, which might result in not being able to get good signal immediately.
You might need to wait roughly 1-2 minutes for the signal to be corrected.

However, if during self-check an error was found, The Set Top box will display the error message, if you still have trouble viewing it, you can request for the signal to be resent automatically by tel. 0-2900-9119