when I overclocked my ram too high, I had the same problem. I had to clear the CMOS in order to get the blinking cursor to go away.
I say try clearing the CMOS and see if it fixes the issue. If it doesnt, and your using 3 sticks of ram, take 2 out, and see if you can get in the bios with 1 stick. If you can manually set your voltage and timings for your ram, then reboot and put the other two sticks in and see if it resolves the problem :)
Good luck.