Hello Murat,
Interesting problem, are you connecting it with USB or are you using a USB-to-PS/2 converter (believe it not, it's not uncommon to see people do this)
Have you tried it on another PC? sounds to me like a driver failure than anything.
Did you try reinstalling the drivers of the keyboard via device manager?
Did you try plugging it into a different USB port?
If the problem persists after trying all of this, then replace the keyboard (like what others are saying)
Interesting problem, are you connecting it with USB or are you using a USB-to-PS/2 converter (believe it not, it's not uncommon to see people do this)
Have you tried it on another PC? sounds to me like a driver failure than anything.
Did you try reinstalling the drivers of the keyboard via device manager?
Did you try plugging it into a different USB port?
If the problem persists after trying all of this, then replace the keyboard (like what others are saying)

