1)Remove the gpu , plug monitor cable to mobo's onboard output
2)start pc - go to device manager - display - uninstall whichever drivers is
3)restart pc - put gpu back
or
1)go to bios settings - set primary display device to PEG OR PCI E
or
1)Update your bios to latest
or
1)update your mobo drivers
or
1)make sure you have connected vga or dvi cable from GPU to monitor not onboard on mobo to monitor