My MacPro, 5,1144.0.0.0, and the graphics card hd7970 have been used for 3 years. Everything is normal. However, I failed to upgrade 12.4. After returning to 12.3.1, the mini DP port has no signal. After the test, I found that the separate DVI works normally. Press option when starting up. There are hard disk options and boot logo. When the minidp port works alone, you can only wait until you enter the system to see the password input box without the boot logo. Press option to see nothing. The screen is blank. Is there any good solution? Do you need to brush the BIOS for MAC of the graphics card once? Thank you ?