Run the Auto-configuration Wizard (tools menu) and apply the settings it gives. Restart OBS (very important)
Notice you are at simple output mode. Do not change it. There's absolutely no need to use advanced unless you know what you're doing.
Now test as is streaming. It should be good.
Change the settings on the recording section and select a Recording Quality different than "same as stream". Test recording. If all goes well, your done.
After each test (start, wait for no less than 30 sec, stop) you may want to go to the Help menu and upload the current log file. Once you upload the file click on the Analyze button and check for common issues you can easily fix.
Restart OBS and test again. Done.