I did have a issue similar to that just recently after some misadventures overclocking.
I disconnected the power, popped the CMOS battery and left it sit for ten minutes, put the battery back in and reconnected power. I made sure to use low voltage RAM...a single stick in the slot nearest the CPU...and to restart I first depressed the reset then the power still pressing down on the reset then after ten seconds released reset then power.
If that does not work try turning off te PSU and letting it sit fo an hour and try again.
Between clearing CMOS and letting it sit I was able to get back into BIOS.
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