My key/mouse won't move when another key is pressed.

[Staneh]

Okay, this is kinda hard to explain.
So, I was playing Garry's Mod, and, I was walking around, but when I wanted to move my mouse, I couldn't, then I tried to press another button, but I heard a sort of "bleep", as sound, and it isn't Garry's Mod itself, I had it with WoW too. How to disable this/fix this?

Many, many thanks if you can help me solve this, this is very annoying.

[Hookerbot9000]

Did something pop up while the game was running and take focus from the window without tabbing you out?

[Dr Nick]

Sounds like StickyKeys to me.

[Drumdevil]

Sticky keys yeah, or very old PS2 mouse/keyboard.