I recently purchased a Canon EOS Rebel DSLR SL1. My 18-55 mm lens shoots amazingly, and I have been using it in auto and manual focus. About a week ago, my manual focus randomly stopped working. The auto focus still works perfectly, which confuses me. Though I move the focus ring in manual, it won't change the picture at all. Is there anything I can do without having to send it in to be fixed?
The current standard kit lens with the SL1 appears to be the STM version which means, among other things, that the camera has to be powered on and ready to shoot (not sleeping) for manual focus to respond. Essentially it's a "focus-by-wire" system, where there isn't a direct physical connection between the focus ring and the actual lens elements, instead the focus ring controls the stepping motor that moves things back and forth to focus the image. If that is the version you've got, then I'd try a couple things to debug the problem.
First I'd make sure that the camera is on and not asleep (push shutter button part way to wake it up). Then if it's still not working, try the same lens on a different Canon camera (any crop sensor DSLR, such as any of the rebels, should work.) If it still doesn't work, then there may be some problem with the lens. If it does work, there may be some problem with the camera body. Either way, you'd need to take it to a professional to get it evaluated/fixed.
If it's not an STM, and you're sure you've got the focus switch on the lens set to manual, and if it's not working, again you'd need to take it to a professional.