Wanting a Windows 10 video driver for ATI Mobility Radeon X1400

OK, I figured this out. Bear with me, this is quite a saga…

There is a Windows 7 driver on the Microsoft Update Catalog. Note that you have to run Internet Explorer as an admin (right-click it in the start menu) to be able to install the plugin to get the driver.

However, if you try to install this CAB straight off it doesn't install correctly; it says a file is missing when you try to install the package. But here's what you can do:

Save the CAB to a folder.

Extract the contents of the CAB.

Open up one of the INF files.

Search for the string "SourceDisksNames"

Look at line below. It probably ends with something like ".\B_72690"

Create the folder with the name after the \ (e.g. B_72690) inside the folder you extracted the CAB into, and extract the contents of the CAB *again* to that folder. This is untidy but it gets the files where it expects them.

Great, right? Not so fast. if you now try installing, it will cause a crash due to a unhandled kernel thread exception in atiumdag.sys. You need to restart into Safe Mode (hold down shift when selecting "Restart", and it's within "troubleshooting/startup options"), and install the driver there, where it won't automatically activate. If the Start Menu isn't working properly in Safe Mode, try using Winkey+R, "devmgmt.msc".

Open up the basic display adapter and upgrade the driver using the "Select a driver from a place I know/Have Disk" option in Device Manager. Select the folder you *first* extracted the CAB to, not the specially-named subfolder. If all went well there should be a compatible, signed driver option with your device's name on it.  Once installed, reboot, and there you go!