If the game is crashing you most likely have some sort of third-party program interfering. Steam and OBS don't conflict with each other and Steam should be more than capable of taking screenshots while OBS is running.
Conflicts with game capture include but are not limited to other capture programs, Razer Synapse (disable heatmaps), graphics mods like ENBSeries and SweetFX, and any type of software or utility that displays an in-game overlay like EVGA Precision, MSI Afterburner, TS3/Mumble overlays, Dolby Axon, Raptr, Overwolf, etc. If you use D3DGear it must be uninstalled completely.