Cant double click on desktop

Hello there.

I got this weird problem yesterday.

It started with that my keyboard (usb with ps/2 extension) didnt work so i changed the batteries. But that didnt work either. Then i unplugged the keyboard, took off the extension and inserted it into an usb port. Then the keyboard worked. But then I suddenly could not double click any icons on the desktop, or enter any sites in internet explorer. But i could right click icons and in internet explorer. I thought i had some virus or trojan so i used malwarebytes, PC Tools Spyware Doctor, AVG Free and a Trojan program, but did not find any malware.

But then i thought.. i can try to use the ps/2 extension on the usb mouse. So i put the mouse into the ps/2 port while the keyboard was in the usb port. TADA IT WORKS! I can now double click, and internet explorer works again.
So i double checked. put keyboard and mouse in usb. Boom.. problem accurred again. But now i also tried keyboard in ps/2 again and mouse in usb. And now i got the keyboard to work in the ps/2, but still the double click problem accurred..
Then i put the mouse to ps/2 and keyboard to usb, then it worked again.

So i have no clue what so ever what this could be  
Please help.

regards from Norway.


system - Win 7 x64 Enterprise, 4gig RAM, XFX Radeon HD 5870, MSI P4N Diamond motherboard