There are a few other common keystrokes that boot into the safe mode menu (ESC, F1, F2, F9, F11, and delete). However, the easiest way to do it, is to start the PC, then as the PC starts to load, hold down the power button and force it to shut down. Then next time it starts up, it should take you to a menu asking if you want to boot normally, last known good config, safe mode...etc.
What are your hardware specs? What is installed in the PCI slots?