Input devices not working at boot

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http://ubuntuforums.org – Well, I'm not sure if this is caused by Ubuntu, but it started to happen after I installed Ubuntu, so I decided to ask here... Sometimes, when I turn my PC it goes to Grub and I cannot use my keyboard to select an OS to boot (I have Ubuntu 13.04 and Windows 7 installed here), so it goes to the default OS, which is Windows 7. Once Windows starts, I can't use my mouse nor my keyboard, not even to turn my PC off (I have to do it from the Power Button)! After turning my PC off and on again it goes back to normal, but still this happens to me about one out of five times I turn my PC on, any idea (Hardware)