MAC doesn't boot after installing Virtual Box

[Nupur]

Hello
I need urgent help. I tried to install VirtualBox on my MAC OS X with windows 7 guest.
The installation of the virtual box and the windows was successful and I also tried to use windows which worked perfectly fine. All of a sudden while using the machine, it turned off itself and now it doesn't start. I tried to start it in safe mode but nothing works.
Any kind of help will be really appreciated. (I do not have the MAC installation CD, the one I got when I bought it).

Thank you

[loukingjr]

Which model Mac? It is possible that you have a hardware failure. Which version of OSX?

I can say it has nothing to do with installing VirtualBox.

[rpmurray]

Disconnect the power cable, wait 30 seconds for the SMC to reset itself, then plug it back in and start it up.

[Nupur]

I tried disconnecting the power cable etc but that doesn't seem to work. Infact a PRAM reset didnt work either.
Yes I fear that it could be a hardware failure. The OS X was 10.10 (Yosemite). Recently I have updated my OS X and my MAC (PRO) has gone really slow since then.
Thank you for the insight

[rpmurray]

All of a sudden while using the machine, it turned off itself and now it doesn't start. I tried to start it in safe mode but nothing works.

Can you give some more details on what you're seeing? By "it doesn't start" do you mean it won't turn on at all? Or do you mean it turns on but doesn't boot to the desktop? If it turns on, what exactly are you seeing on the screen?