For some reason, every few times (let's say every 5 times) I restart my Mac Mini (running MacOS High Sierra 10.13.3, on an SSD), the startup screen will get stuck on the white loading bar with a black background, with the white bar at 100% full and just sitting there for minutes (the longest I left it on that screen is about an hour, and I wasn't willing to wait any longer). If the startup screen is stuck, and then I force my Mac off and turn it on, then it just gets stuck there again, once the loading bar reaches 100%. The only way to bypass this is to reset my Mac's PRAM. Then when I start up the Mac again, it loads fine. Why does this happen? And how can I fix it? Unfortunately, I'm not sure when this started happening, since I rarely restart my Mac, except when I update it. I only Sleep my Mac every night. My Mac's memory is actually brand new (it's a few days old), and I have already ran a Mac Hardware Diagnostic anyway, and it said there were no problems.