Can't boot OSX or Windows

[Blast12345]

MBP 13" 2012 - Base model

So, in some strange turn of events, I am unable to boot into either OS.

I installed Windows 7 under bootcamp. All went fine, but today Windows will give me a BSOD so quickly I cannot analyze it.

Most of the time, I cannot use the option key to get the bootloader. I click and hold option like no tomorrow, but it just boots into the seemingly faulty windows.

When I was able to get into the bootloader (or whatever you wish to call it), it would only list the Windows partition/option. OSX would not show up.

Can anyone shed light on my dilemma?

 

[simsaladimbamba]

Have you tried any of these steps?

Mac doesn't boot

Resolve startup issues and perform disk maintenance with Disk Utility and fsck

Troubleshooting: My computer won't turn on

A flashing question mark appears when you start your Mac​

 

[Blast12345]

I hold down buttons at startup (tried shift and P+R) and after a long grey screen, the faulty Windows starts booting.

No flashing question mark or anything appears. It is just a long grey screen before it boots into Windows.

I did get back into the startup manager, but it again only shows windows. Should I find a Lion disc and trying using that?