We trust that you have already given your unit a full charge and the charge light was on indicating it was taking charge the whole time. If you have not, please check this link on what to do when your unit is not taking charge.
If the unit has already been charged fully but is still not turning on, you need to format your card. If you have a newer model, try connecting it to your phone via CycliqPlus app and format from there. If you are unsuccessful or if you have an older model, please format your card using an SD card adapter. You can follow the video instructions on this link here.
After formatting, turn the unit on by pressing the power button for at least 1 second.
Note: You can also try turning the unit on without an SD card, For newer models, please also perform a master reset before turning it on and see if this helps.