After inserting the graphics card "ATI Radeon HD 5750" to the motherboard "M2N-MX SE Plus", the computer cannot operate normally and the screen shows eternal darkness. Is the graphics card compatible with this motherboard? How can I fix the problem? Any BIOS upgrade needed?
This is not a graphics driver issue. Once again, we're dealing with a PCI-E 2.1 graphics card being installed on a motherboard with a PCI-E 1.0/1.0a slot. And yes, you probably do need a BIOS update. Given the age of the board and the date of the last BIOS update (11/4/2008), it's possible the card will remain incompatible.
You need to go here, select your OS, and expand the BIOS portion. The 0602 BIOS is the most recent, so download it. Also, in the BIOS-Utilities section, get the update tool.
Again, I am not certain this will enable compatibility with that video card. If it does, great. If not, consider an older generation, PCI-E 2.0 card, such as an HD4850 or something from nVidia.