Windows 8 – Blue Screen.

Windows 8 – Blue Screen.
I bought new desktop (HP) with pre-installed Windows 8. I was trying to add some softwares and by just plugging-in the USB device (external harddisk containing softwares) the icons gradually disappeared when I clicked each one of them.

Now the whole screen is blue, only the mouse’s arrow is visible and moving. I’ve tried to restart but nothing happens. I would like to format the disk and instal Windows 7 that I am familiar to but unable to format it.

Any suggestion to reclaim my brand new PC is greatly appreciated.