bootloader - Android tablet won't reboot after rebooting using volume and power buttons

I am using a 7" Smartfren tablet called S7.

I was following this tutorial. When I got the last part about the bootloader, I turned my device off. I tried to reboot using the volume buttons and power button, but it won't open up. Also, it cannot be seen by using the command adb devices. Thus, I can't use any adb command to access it. What am I doing wrong?

It is recognized by my laptop as Android Bootloader Interface. So, it means that it can still be detected by my laptop, but not when using adb devices in cmd.

Edit #1: I tried the fastboot devices command, and it just returned an empty line. I guess it means that nothing happened.

Edit #2:
I'll tell you its current status. It can't be normally rebooted, but when you plug it in, it shows that it is charging. Then if I put it back on its case, complete with box and all it heats up meaning it is still functioning and is turned on.