When my computer starts it shows the messege which say (unlock keyboard).what can I do
To solve that problem?

Check these three things:

1 - Make sure the mouse and keyboard connections are correct. Many times plugging in a PS2 mouse in the keyboard connection makes the computer stop with a keyboard problem. If you are using a USB keyboard, make sure the PS2 keyboard option in the BIOS is disabled or set to ignore.

2 - Make sure none of the key are stuck. If one of the keys is stuck - like it's being pressed - the computer may stop with a keyboard error.

3 - If the keyboard has an actual LOCK key button or switch on it, unlock it.

You can also try another keyboard - just in case the one you have is faulty. :)