Cannot boot my mac mini (2011 2.5Ghz 4Gb Mavericks)

Hi,

I have a mid 2011 Mac Mini (i5 2.5Ghz, 4Gb) with Mavericks running on it. It was connected to a Samsung tv through vga (mini display port). Until yesterday everything was running fine.

But today, for no reason, when I press the power button, I only hear the boot audio but no display. Then I connected it to another monitor with hdmi, I can only see the apple logo with the progress indicator below it, but it just hangs in there i.e. the progress indicator keeps running forever.

I haven't upgraded or changed anything on the mac mini.