Exported file unplayable

Hello everybody

Strange things happen (all the time)

Totally out of the blue and without any changes in my software or hardware, after I export a file (MP4), the exported file does not play in any media player. For example in Media Player Classic I use, I get the message "Cannot Render File".
First I updated DaVinci in the latest version (I was using 16). Nothing changed.
I installed fresh Codecs, I tried exporting in .MOV, I tried exporting again older projects, I rebooted my PC.
Finally I installed version 17. Nothing worked.

Any help would be very appreciated.
Thanks in advance

Which version are you using now?

first things to check with a file that won't play...are you sure the export finished?
does it have the correct extension?
can you bring it back into Resolve?
can you repeat this error on another project?
can you repeat this error using a single clip from current project?