lexvegas is correct; it sounds like one of your modifier keys is stuck (most likely the Ctrl key based on your description).
Obviously, this can happen through mechanical means such as the key getting physically stuck from a sticky liquid, dust, paper, etc. Check that nothing has fallen in and that the key physically move up and down freely.
Another reason that a modifier key can get stuck is from software. Sometimes when you are holding down a key and the active window changes in just the right way, the key-up message (
WM_KEYUP) that is normally sent when a key is released can get lost and/or misdirected, which then causes the system to think that it is still being held down.
Try pressing it a few times to release the key. If it is a software lock, then simply pressing and releasing it should resolve the problem. If it is a physically problem, then you will notice that it doesn’t pop back up (or go down in the first place) and can then address it. Either way, make sure to test both keys since most keyboards have left and right Ctrl, Alt, ⇧ Shift, and ⊞ Win keys. (in fact, whenever I notice any strange keyboard behavior, I instinctively just mash each of the eight—four pairs—of modifiers a couple of times).