Sometimes I am able to use my USB keyboard perfectly fine; other times, it behaves as if the Ctrl key is permanently pressed.
I don't think it is a hardware problem, as the problem stays even if I remove the external keyboard, and it only goes away if I restart the PC or start the on-screen keyboard. My antivirus didn't show anything and don't have sticky keys on.
Why is this occurring, and how can I solve it? I'm running Windows 7 on my laptop.