If the jobs are grey, then they are queued. It is almost always best to leave these to execute, otherwise you will lose your place in the queue for no benefit (the job will just queue up again, but at the end). If the jobs are a light blue, then they are paused and this means that an upstream step was problematic. Fix that tool with a re-run and you will be presented with the option to "Resume dependencies" which means to re-queue downstream jobs with the new output as input.
More about dataset states is in the Galaxy Support wiki, Section 2.6 https://wiki.galaxyproject.org/Support#
Thanks, Jen, Galaxy team