So I tried running Lubuntu from a live USB, and it worked, except for one thing: it couldn't use Wi-fi without the drivers, so the only way it could access the internet was through USB. Now, that would be okay if I weren't going to connect an external keyboard, because the laptop only has two USB ports, and one would be used by the live USB stick. So I looked in "additional drivers", and it did let me download and "install" the drivers, but since they aren't installed anywhere outside RAM, they only stay for as long as the laptop is turned on. Except it seems you can't install drivers without restarting, so I would have to install the system somewhere writable in order to be able to install the driver. I tried to install it on an external hard drive, and not having more than two USB ports, I couldn't stay connected to the internet while installing. So after installing, I ran the full upgrade program, and then, without first restarting, I tried to install the driver. And after that, I restarted.
The login screen was missing a mouse cursor, but I could type the password. And the background image looked like it was bigger than the screen. Pressing the left mouse button made it so I couldn't type more, so I had to turn the laptop off and on again. Typing the password and pressing enter would let me to a black screen, sometimes with random colours in the bottom right corner. And that black screen, or mostly black, would stay like that forever. The desktop wouldn't appear.
Now, I've used Ubuntu before on two other computers, so I tried some control+alt+f-number keys. That would give me some terminals that let me log in, so I tried typing startx in one of them, and got a black screen and a mouse cursor. I could right-click the desktop and get some more options, but they would just tell me some default command couldn't run (sorry, I didn't write the message down). I'm pretty sure the first time I did that, there wasn't a menu in the bottom of the screen. But one time I tried startx & xterm, and I didn't get an xterm window, but I did get a menu in the bottom of the screen. But no desktop background, just Blackness.
Then I tried looking at the options in the GRUB menu, and booting the other kernel didn't change anything. Then I tried again with the "old" kernel, and it somehow worked for a couple of times. Then it somehow stopped working, so now recovery mode is the only way I can get to the desktop. The problem with that, though, is it keeps the screen at full birghtness, which isn't very pleasant to look at.
Then I tried startx and xterm again, and this time I didn't get a menu (or a terminal, for that matter), just useless black desktop where I can't start applications. The commands openbox and openbox-session show an error message about not being able to open the display from the environment variable DISPLAY.
So is there something I can do to get both the screen brightness changeable and the desktop working at the same time? I guess as a last resort, I could research how to start a menu and startx at the same time, but the man pages don't seem to give me enough information to do that, especially when I don't know what the menu bar in lxqt is called. But if it's possible to get things to work normally (not having to run commands every time I turn the laptop on), that would be better.