Sometimes it may seem like finding a theme is impossible, but don't worry. Sometimes you need 2 seconds, sometimes 2 hours or maybe 2 days to find a theme. If you're even able to find a single idea that fits the theme that's a win in my book.
This theme right now - Overheat - it doesn't have to be a pc overheating. Maybe it's a car engine that overheats? Maybe it's a volcano that's overheating? Maybe you just have something overly hot? Maybe it's a man going through a desert without water that's overheating? There are a lot of possiblities and no worries if it just doesn't ring that bell immediately. It happens to everyone sooner or later. I often feel like I don't have any good idea and sometimes I just find that sweet-spot.
In either case good luck! It's a process, so don't give up. If you want it, you can do it!