When I try and use the level-up screen for the first time the game always crashes, with a message about how it was trying to access grapics hardware. I tried running it in adminstrator mode, but it still crashes. I'm also using the Jade Empire In Style mod.

Well, first of all I would try uninstalling the mod, to see if it could be the cause of the crash.
Also you should provide information about your system (hardware, OS, etc.): it is not easy to help you otherwise.
That said, if you are using Windows 8 or later, I think you should try setting the game to run in compatibility mode for Windows XP.

This resolved the level up crashes for me. Not ideal, but I've been able to continue to play the geme:

I took this from jadeempire.fandom.com/wiki/Crash_Fix

1. Go to your Jade Empire installation folder.

2. Open the " override " folder.

3. Find the " apperance.2da " and open it in any text editor of your choice.

4. Look for the line with " WildFlower_f " in this case it is line 40

5. Now replace the " N_Wild_ " in the second column to " N_Dawn_ ".

6. Save and close the file.