Windows 8/8.1/10 Cant move UI in game

Hopefully not going outside of my remit by responding, but I'm a bit of a tech nerd and I enjoy the challenge of troubleshooting

Logic would dictate that if the only significant change you've made is your mouse, then the mouse is the problem regardless of how it functions in other games.

The client ML uses is probably? just a customised version of the original v62 client, a piece of software designed to operate on Windows XP and programmed specifically with the capabilities and established practices of the time - as you can gather, this means modern devices won't always be perfectly compatible (though usually are). Despite their obvious extensive knowledge of the codebase (or just HEX editing? I'm not sure how client mods are done nowadays) the staff team likely don't have access to the entire source code of the launcher, so the support available there will be minimal.

That said, you've not given much to work with. A 'HID Compliant Mouse' signifies an input device which doesn't have specific drivers (think the difference between a Razer vs. $10 amazon mouse). Nearly every mouse can default to the standard drivers that all USB mice are capable of operating with, like yours, but most decent ones install their own drivers through PNP. What you've told us is basically that you have a mouse that isn't working without any useful details.

My assumption is that your mouse is, in some way, not properly compatible with the client.

Assuming you're not willing or able to invest in a slightly better mouse, then I'd advise you to do the following:

• Give your system specifications - OS, CPU, GPU, mouse brand/product code (usually mice have some indication of their branding), etc. For fomatting's sake, use [ code ] tags.
  
• Provide a bit more context - did your old mouse work perfectly fine with moving UI elements? Are there any other mouse-related issues you face in ML? Do you play any other games that haven't had a client update since the 00's?
• Think of any "significant" system changes you've made since installing your new mouse. Any software you've installed, potential hardware changes, updates etc.

As this isn't an issue I've personally seen before, I'm guessing your mouse just isn't natively compatible, but that doesn't mean it can't be fixed. Provide the above and hopefully I can help! Or, if someone more knowledgeable is around, they can give you a simple solution that I don't know about.