Spacebar presses won't register when other keys are pressed down.

[Aapo]

I noticed that some key press combinations won't work on my keyboard. I wonder if this is a operating system issue or keyboard issue.

When I press down A + S and press spacebar, spacebar won't register.
A + Spacebar register as does S + Spacebar.
Spacebar doesn't register while S and D are pressed down.
A + W + Spacebar works.
W + D + Spacebar works also.

In some games this means that I can't jump/shoot southwest or southeast. Anyone else have this same problem? Any ideas how to fix this?

Here's a website which shows which keys are being pressed:
Keyboard Checker | The best online keyboard tester

 

[Aapo]

I noticed also that when I hold down A + S + Spacebar OR S + D + Spacebar, after a while I can hear sound *pup*, repeating every second as long as I hold the keys. This seems to point to software issue.