With something like a back injury you have to be conservative and use a process of elimination; I just went through this. If it's a milder muscular problem this will be sufficient to clear it up.
Start by eliminating any exercises that directly cause pain, until the pain goes away. Work around it.
If that doesn't work and even indirect exercise aggrevate it, take a complete break from workouts for 7-10 days to see if that clears up the problem. Don't worry about missed training, a break's good for the bod & CNS in general and can help you progress once you return to training. With the back problem I had, a complete break from training worked, whereas trying to work around the problem while continuing to work out didn't. On the 9th day of rest the pain almost completely disappeared.
If that doesn't work it's probably more serious; then see a doctor.
Once the back is better, you have to avoid whatever caused the problem (heavy deadlifts in this case). Either continue with deads or find a substitute, but if deads are done go with high reps and less weight-you'll still get excellent results and will still add strength, without straining the bod. If this doesn't help, you have to find a substitute exercise and avoid deads altogether; something like hypers.
As far as cardio, if you're only doing short-term bulking once in a while you could stop the cardio totally and resume later. If you're bulking on regular cycles and want to maintain some cardio you could moderate the amount of cardio in between weights.
