@mumblebaj so trying a new SD CARD could resolve the problem?

Can somebody help me! I just bought a Raspberry pi 3 and installed Raspbian full on it. I also installed MagicMirror on it.
When I first ran the raspberry pi everything worked fine but since I restarted the pi it won’t start up again and the green ACT light doesn’t light up anymore.
I tried to reinstall the software on the SD card with the official raspberry pi imager v.1.4
I’m now trying to use the official SD card formatter software from the SD Association.
if that doesn’t work I’m going to try another sd card.
I have done some research on google about the subject but all answers tell you the same thing. they ask you if you have installed the right power supply.
if you have the HDMI plug in the HDMI0 port and if you have an operating system installed on the SD card which I have using the raspberry pi imager.
if you have any tips please leave them in the comments of this post!