mid 2011 imac grey screen on boot with no bluetooth keyboard support

Hi,

My mid 2011 imac has been extremely slow lately and yesterday it froze so I held the power button to turn it of.

When I turn it back on it chimes and then gets stuck on a grey screen with no apple logo and will not go any further.

I have tried to boot into recovery or safe mode but no matter how long I hold down the keys it will not go past the grey screen.

What can I do to get the computer to boot?