Could be your card, your monitor, or your cable.
Before completely freaking out though, check and make sure there is nothing magnetic anywhere near your monitor that could be causing interference.
If that doesn't solve it then check your monitor cable, make sure there are no bent or loose pins in and, and make sure it is securely plugged in.
Next, try another monitor (borrow one if you have to).
If the picture if fine on another monitor, then it's your monitor.
Check your videocard, make sure it is seated properly and check all connections.
Update your video drivers.
If you do all of these in order and your pic is still screwy, then yes, it's your card.