Shift key not work when required password time.

Hello everyone,

I am using Macbook Air mid 2011. and its have mac osx yosemite. Every time all of the keyboard keys working but . I put6 my login Password Hasib141. But when i enter the password shift +h but it has still small later , shift not working i press Shift_ h but itsa giove me only small h. Its very strange so how will i slove it. Whn i write on notepad and there is shift key working good and give me the capital latter. that time i press Caps lock then enter h and after caps lock off and press rest of the password. Then i can log on. SO what is the problem, Please Help me .

Sorry for my poor English