1. You didn't post a log.
2. You don't tell us what webcam you're using.
3. You haven't told us what the webcam settings in OBS are.
4. If you had posted a log, we would know if you're using Studio or Classic.
Without following the basic forum rules and having the courtesy to read up before you post, you have failed to provide the basic stuff needed to help you.
At this point all I can recommend updating to the latest drivers for your webcam (or reinstalling them if they are on the latest), removing and re-adding it to OBS (Make it a Global source if you're using Classic), and don't try to use the webcam in OBS and another program at the same time. Hopefully it'll work.