I have a computer that seems to stop running after 15 to 20 minutes and then I have to log in again to start it. How do I just let it run?
It’s unclear what you mean by “stop running”.
It is powering completely off? Is it suspending? Are you merely seeing a lock screen? Or something else?
You will get the best help if you can clearly describe the problem to we who cannot see it.
We don’t know what your computer is running, as you’ve not told us.
On my machine (Lubuntu 25.04), the default was for screensaver to kick in after 10 minutes; which is way to short for me, in fact I’ve disabled it. I’m not in a public office, so I’m happy with physical security alone here (on a Lubuntu/LXQt system the screensaver also acts as screen locker)
My screens would also power off too (power settings), which I didn’t want, so that too was disabled.
If you’re having your screen locked due to inactivity; change the settings for it.
If you’re having screens turn off, change the power settings for it.
For us to provide specific help though; you need to tell us what you’re actually using (Ubuntu 25.04 Desktop? Ubuntu 24.04 LTS Server? or like me Lubuntu 25.04? the options are essentially the same for all, but where they are in menus & wording for them varies)