I had Windows 8 installed of my Mac for a while, using Bootcamp. However I wasn't happy with Windows 8, couldn't get proper drivers and it was being a pain, so I went back into Bootcamp (Via OS X) and removed the Windows partition.
Whenever I boot up the Mac now I just get a black screen that says there is no bootable device, please insert a disc and press any key.
Any idea how I can make the machine automatically load OS X instead of having a fit?

If I hold Alt when I start the machine then it's hit and miss whether it gives me the boot menu to load OS X from. Obviously this isn't an ideal solution as I don't want to have to constantly re-start the machine and hold Alt until it eventually works.