I assume "I can't use my keyboard, since it doesn't connect" is because it is a bluetooth keyboard.
Chances are you have something more serious that Safe Mode may not work, HOWEVER, if you cannot use the bluetooth keyboard, then you need to plug in a USB keyboard and try booting holding the Shift key.
I'm not sure that will actually work, but if bluetooth keyboard not functioning, then you need to try a USB keyboard if you think it will help.
Alternatives. If you have another Mac AND if both have Firewire ports, you could try putting the non-booting Mac into Target Mode (again you may need a USB keyboard). Boot holding Command-T to put the Mac into Target Mode. Connect the 2 Macs via Firewire cable. The Mac in Target Mode should appear on the other Mac as an external disk. You should then be able to use the working Mac's Applications -> Utilities -> Disk Utility to verify and if appropriate repair the Target Mode disk.
If all else fails you may need to restore your system from your most recent backup.