I have Lightroom 3 running on an older machine (Windows Vista). I used a Canon EOS Rebel XS camera, and recently upgraded to a Canon Rebel EOS T5. I was able to import my raw files from the Rebel XS into Lightroom, but it won't let me import raw files from the Rebel T5. I've upgraded Lightroom 3, but do I have to simply get a new, more up to date version of Lightroom? If so, which one?
Your new camera requires at least Lightroom 5.4. Adobe no longer sells Lightroom 5. You can upgrade to Lightroom 6, or subscribe to the creative cloud, or you can download the free DNG converter and create DNG copies that you can use with the software that you have.
You can purchase LR 6, but it won't run on Vista. The other option Jim suggests might work if the DNG Converter runs on Vista, still. I'm not sure. You can try and download the DNG Converter installer from the following link, run the installer, then run the installed DNG Converter to convert the T5 CR2 files to DNGs then those DNGs will open in the older LR: http://www.adobe.com/downloads/updates/
If the DNG Converter says it isn't compatible with Vista then you're stuck until you upgrade your computer's OS. The other thing to keep in mind is that LR 6 is 64-bit only so besides needing Windows 7 or newer, it also needs to be a 64-bit OS.