Can't use keyboard and left mouse button simultaneously

I can't use any keyboard keys and use the left mouse button simultaneously; there is about a 1 second delay after I stop pressing any keyboard keys until the left mouse button starts working again.

This makes it barely possible for me to play games such as 'Team Fortress 2' because I can't press spacebar+ctrl+mouse1 to rocket jump (Note that the problem happens all the time, not just in games).

• This happens with every key on the keyboard except for the SHIFT, CTRL, Fn and ALT keys.

• The problem remains regardless of whether I'm using an external/inbuilt mouse/keyboard.

• I have used this laptop without having this problem in the past.

I have already tried going to the control panel > change mouse settings > 'Device Settings' tab> Settings... > PalmCheck-Enhanced ACM and moving the slider in PalmCheck down to 'Off'; this did not work, of course.

I am running Windows 7 Home Premium edition
on an HP Pavillion dv6 Notebook PC;
AMD A6-3410MX APU with Radeon HD Graphics 1.60GHz;
8GB RAM
64-bit OS