Boot issue

[RichardBeer]

This issue was almost certainly caused by me but I have no idea as to what the issue is.

I firstly partitioned my drive in order to install Linux Mint/Ubuntu via USB drive.
After installing Ubuntu, I was met with a none bootable partiton for ubuntu and an issue with booting. Removing ubuntu did not fix this and nor did the problem stop when I tried switching out drives.

The computer issues one beep and the screen stays black.
Holding down the I/O button for 10 seconds and rebooting presents a black screen and no tone. This happens until the fourth attempt to turn on the mac.
On the fourth attempt, the mac boots up as normal.

I've tried resetting the PRAM but as the machine needs to reboot twice to do this and cannot successfully without the tone, this is impossible.

Does anyone have any ideas what the issue could be?

I'm using OS X Lion and my specs are in my signature.

Thanks!

 

[RichardBeer]

The only thing that I can think of is that I have somehow changed some firmware setting, like the boot order, but I have no idea how that would happen.