OSX Startup disk disappeared?

Thanks to anyone who might be able to assist me.

Today, I was using my Mac when it started to act strangely, so I restarted. On restarting it booted directly into Windows 7 (I have my OS X and Windows 7 startups on separate SSDs). When logging into Windows it gave me an error message saying that the OSX disk was not ejected properly and since then I have not been able to restart into OSX.

If anyone had any pointers as to how I might be able to get back up and running that would be great.