These days, there’s not a whole lot of difference between modern (and even not-so-modern) flat-screen TVs and computer monitors. For all intents and purposes, they’re more or less the same thing, just intended for different primary uses. The biggest difference you’re likely to find between your TV and a dedicated computer monitor is the inputs. Your TV likely has some additional RCA ports you probably won’t need.
With just a few minutes and, potentially, an accessory or two, you can hook up your old TV to your computer, and upgrade your existing monitor to something larger, or add it as a second display. If you’re lucky, you already have everything you’ll need to get started. Provided your computer uses HDMI outputs, simply connecting your TV with an HDMI cable and powering it on should do the trick. Some computers, however, utilize a display port instead of HDMI. They look pretty similar, but the shapes are different. No matter how hard you try to cram an HDMI cable in the port, it won’t fit. If that’s the case, you’ll need a simple HDMI adapter to convert the signal.
If your computer happens to use DVI, even with an adapter, you’ll pick up video but not audio, and you’ll need a separate set of cables to send the audio signal (via Gadget Review). Once you’re connected, make sure your TV is switched to the correct input, and you’re off to the races.