White screen after switching back from windows

I installed Windows 7 on my late 2009 iMac 27" using boot camp assistant. It did not run stable, so I wanted to switch back to High Sierra and delete the windows partition.

However, I cannot boot into High Sierra now. The apple logo shows up as usual, but the progress bar would stuck at roughly 60%. After some 30 seconds, both the apple logo and progress bar disappear and only a white screen continues.

I have tried to boot into recovery mode so that I can wipe the SSD and re-install Hight Sierra. No success. Same white screen.

I cannot start in safe mode either.

I have put in an SSD from another working iMac and reset the NVRAM. Still cannot boot up into the MacOS, safe mode, or recovery mode.

Anyone has experienced the same? Any solutions?

Thanks for sharing your thoughts and tips.