Black intermittent display

Hello,
My pc is turning on and is booting to the desktop but by displaying intermitently during booting and no more display on desktop. The only way to see anything is by turning off and on the monitor to have 1 or 2 second of displaying.

The only thing that changed since the last time I used this pc (a few hours) is that i only removed a fan..

All drivers are up to date
I tried my monitor on other pc and it worked fine
I tried clearing CMOS but didn't changed anything
I also checked all possible connections

Thanks for help !