out of sync is usually a monitor message. It sounds like your monitor said to the computer it could to something it actually couldn't. If the monitor says it can, MacOS (either of them) doesn't check. So now your computer is absolutely sure your monitor is doing something that the monitor absolutely can't.
Try booting without the monitor attached, then sticking it on once the machine should be booted. Perhaps you'll get 640x480 or some usable resolution. Other than that, your best bet would be to zap your PRAM.
I'd like to think there's a monitor resoltion fixing solution better than this, but I don't have it.