No display but mobo runs

Hi, just now I installed the Nvidia 310.70 driver update, after a restart, the desktop loaded, then I wanted to use the internet, but before that, my PC autoamtically restarted, and there's no sign of display at all.

I am using the MSI 650 TI Twin Frozr. The fans of the GPU is spinning as usual, but there is no light, until about 30 seconds later, the fan stopped briefly and lights came up.

Also, the case fan for my chassis also ceased to turn. It was as though there was not enough power.

For my PSU, I'm using a Seasonic G Series 550W.

Anyone can point out the problem?

EDIT:


On a side note, I managed to get it work, but I have no idea what did I do, but what I do realise is that I did not insert the GPU. I used the VGA output from my mobo directly. I uninstalled the driver, restarted the com with my GPU inserted this time, redownloaded the driver (As i suspected the driver installation file to be faulty), and reinstalled the driver again.

Again, after the restart, like 20 seconds into the desktop, the system auto restarted, and there's no display again