I'm not talking about mouse lag or speed, I can't use my mouse at all in Skyrim, not even in the start menu. The keyboard works, I have no gamepad plugged in. The mouse cursor is invisible, but it shows up when I move it to the top of the screen. When I left click(at the top of the screen) I can drag the Skyrim window around(despite I checked fullscreen mode). In windowed mode the mouse doesn't work either.

Help is much appreciated.

Disable the gamepad in the settings menu, if you haven't already.

The settings menu in-game? Apparently I can't access it with ESC in the opening sequence(the cart ride) and without a mouse I have no way to get past the character creation screen. Is there a console command to open it?

Get rid of any "Mouse Animation" settings at all in Windows.

(Mouse "Trails" being among the very worst of all.)

I have none activated.

Then try disabling the gamepad settings in the INI file.

Mouse still doesn't work :/

I used the wrong .ini file(the one in the steam folder), not the one in \my documents to disable gamepads.

It works now, thank you very much.