Shaky/Jittery/Flickering Monitor: Bad monitor or bad graphics card?

It could be the cable - a bad cable or loose connection can absolutely cause flickering. If it's a DVI connector, take a look and see if any of the pins are bent. When that happens to me I often am able to straighten them out enough to work using just a paper clip. If that doesn't seem to be the problem, it probably wouldn't try borrowing another cable from a coworker, to test with. If that doesn't fix it, see if someone will loan you a monitor for a few minutes. If it comes down to it, swapping a video card is not very difficult at all. once you have it. You just open up the case, and unplug the big card with the fan on it (you'll have to unscrew a screw on the end first), put the new one in, and screw that in. Close up the case, hook up the cables, and turn on the computer. Depending on driver availability it might boot into a lower res mode - either way go to the vendor's website and get the latest driver. All done.

But before you think about getting a new video card definitely test replacing all the other components that you are able to.

If the monitor seems to be working, the pins are in good shape, and it still is flickering, also try removing and reseating the video card before replacing it. At least back in the day (PCI) the cards used to be a super tight fit and occasionally it could push the card up and out when my computer was moved around enough... But, if that doesn't work either, well - you'll have had a little practice getting the card in place. Warnings: it sometimes takes a lot of force to seat cards, doing this may help you with a dry run. Since this is something new to you, I'd just note that you should make sure your computer is off before you are removing / installing hardware. You can test stuff with the case open (and do), but power off before pulling out hardware.

Good suggestions above. Check that you don't have electrical stuff nearby the monitor: that can cause similar symptoms. Try moving the monitor further away as a quick test. You might also try plugging it into a separate electrical socket in case the power supply is a bit wonky.

Definitely replace the cable first. I’ve had this happen with cheap DVI cables, and also with cheap mini-DVI adapters (the latter issue will not be yours).

Before you start swapping/reseating video cards, you should do the simple, easy stuff. As mentioned above, try the monitor self-test (without the cable attached, if that's an option). If it still does it, it's the monitor. Next step would be to find another working computer, monitor and cable. It doesn't have to be the same kind. You must know someone with a computer? A laptop? A TV with a computer connection? Plug the suspect monitor into the working computer, and vice-versa. Then you can rule out the cable by swapping it. This should point you to the failing component without violating any warrantees.

sigh. turns out it was the monitor. it straight up stopped working this morning. went black and would turn on dimly for about 1 second. sadly went to best buy and bought a new monitor and it works fine. so, monitor it was. whee.