|I'm assuming this is a desktop computer.|
Most laptops DO NOT have a video CARD - the video adapter is usually built into the mboard and cannot be removed
The computer video output is processed through a chip on the video adapter to produce the TV-out signal, to conform to legacy TV standards, at a vertical refesh rate of either 50 Hz (e.g. PAL or Secam standards) or 60 Hz (North American standards).
Make sure the card is seated all the way down in it's slot.
Try removing the card, wiping off it's contacts, installing it again.
If that doesn't help, you may have damaged the card's circuits.
When you have an ATX family computer, you MUST remove the AC power to the case / power supply whenever you are going to be plugging in or unplugging the video card or any other card, or the ram, or the wiring connections - there are places on the mboard that are always powered as long as the power supply is receiving live AC power, including some of the contacts in slots.
Video cards are easily damaged if you didn't do that. AGP video cards are especially easily damaged because the AGP slot and the card have two vertical rows of horizontally staggered sets of contacts. It's also important for the video card, especially an AGP video card, to always be fastened down at it's bracket before you try booting the computer.