Boot loop for over 12 hours

Hey there, can someone help me out? I have a pc and it started boot looping a while back, sometimes it starts up after 2 minutes, but sometimes it takes over 12 hours. I have tried a lot of things but cant seem to figure out what the problem is. Do any of u have an idea? I tried fiddling with bios, doing cmos reset, seeing if the motherboard and other internals worked, reinstalling windows but it was all as it should be, just not starting normaly