Letter ''Y'' not working in keyboard

i have a computer i used for almost 2 years, not yet formatted and no problem in installing any program and adding hardware like new DVD player and RA memory and extra fan.

Since last last night as i remember i off my computer like a typical off but then in other day when i open my computer is normally good they show the window and other program.

then when i go to microsoft word my letter ''Y'' is not working or not showing everytime i type, but the cursor or the line blink is moving as i click any character with also a letter ''y''.

my problem is goes like this.. famil <------( when i put the letter ''Y'' is not showing but the cursor is moving as i typing the ''y''.)

i try to change my keyboard but they have same problem the letter y is not showing too.. i put my own keyboard in the other computer the letter ''Y'' is good what i mean is when i typing a words with letter ''Y'' is showing it using my keyboard in other computer.

i try to print the page that i type even thou that have no letter ''y; to see if maybe the letter ''y'' is hidding but when i was print the page is not there no letter ''y'' again.?

but when i open in DOS ( Black window) to try the Letter ''y'' is in there
is good like this..

C:/> family <---- the letter ''y'' is showing.

but in other program was no letter ''y''. i have internet connection when i search in any browser the letter ''Y'' is not working again?

can you pls. help me and give me idea for what the problem of my damn PC.