I plugged in an external HD I first used on a Windows machine then the whole computer freezes except for the mouse cursor. I tried turning the computer off by pressing the power button but nothing happens.

So I unplugged the power supply and removed the battery. I then put the battery back in and plugged in the power cord. I tried turning on my computer but all that appears on the screen is a white page. And the sleep light keeps flashing by 3 blinks at a time.

I tried booting the computer holding down the option key. and I tried booting with the OSX disc. But these methods failed.

Any ideas on how to solve the problem?