I assume that you have tried to activate uppercase with CapLock and Shift keys. Although it is not very likely, this situation might be caused by the StickyKeys feature. Press both Shift keys at once, in order to deactivate this option. This is the only solution you can try in the given situation and the most possible cause is a hardware issue. In this case, I would recommend you to contact your local retailer and ask for a keyboard replacement.