When I turn on my computer, the monitor goes blank and the message "OUT OF TIMING V:58Hz H:92kHz" (although its possible that the numbers change, I haven't checked). The grub menu does not appear (meaning that I cannot boot into windows, which is the main reason this is annoying me), nor does the loading bar. After a short wait, the login screen of 12.04 appears. The same error appears when I press alt+F1-6 to enter a tty. Please help!!