Hello,

Many of us use OBS but it could not work while you flash your PC because of the absence of drivers like Nivedia Ge Force or you have enabled gaming mode section.

I am not here to restate the solutions that where mentioned but some alternative solutions if you are not going to get the risk for install an adequate driver after the solo flash of your PC:

1 - Use of Monosnap:

It could be feasible as a chrome extension to record your screen. Alternatively, you have to allow access to extension to the microphone to start recording.

2 - Use your mobile camera or external camera to your front of PC:

It is another solution to record your work then it could be a good solution to opt out of OBS but you still need to install required drivers for further uses.