Up+Left Combination Not Working?

Last week, I made a fresh installation of a Windows 7 x64 copy on my PC. I haven't touched it ever since until today. Installed some games, like AC Revelations. When I tried playing it, I found that the Up+Left Arrow key combination on the keyboard was not working and when I pressed them, the speaker gave out beeps just like when you press so many keys at once. All other combos works perfect but the up+left doesn't work not only in-game, but also outside games for general use. Whenever I press the keys, continuous beeps are being heard. I tried restarting my system and unplugging and re-plugging the keyboard. It's not working, and the problem's still there. I tried downloading KeyboardTest program and when I press the combo, it's not appearing and the beeps starts.