After not-using it for a while, I wanted to draw with it again, only to find it broken!
I switched ports multiple times, and the installation screen showed up after restarting. It gave me some error about it may not work on XP, but I got that when I first installed it too, and it worked perfectly then.

Now you might think it's just broken, but it isn't!
It works perfectly on the user selection screen, before I'm logged into XP.
As soon as my personal settings are loaded it just stops functioning.
I've run through all the settings that could prevent my tablet from working, but it's all set up correctly.

My tablet is a Lifetec 9310.
I really want to draw again

Sounds like you might need to reinstall/update the drivers

I installed the latest driver from the site, and whereas before, the tablet stopped working the second my settings were loaded, it now stops working a few seconds after my desktop loads. So it functioned a short period of time after I logged in.
An improvement, but not that big of an improvement

Check your mouse and tablet settings. There might be a mouse override setting, probably in the tablet settings.

I'm telling you, I checked every single tab, everything is configured like it should be (and like it was when the tablet was still working)

Is there a drawing program that came with your tablet? I find that sometimes when mine doesn't register all I have to do is run the drawing program that came with it and it gets going again. Usually new drivers work, but not always.