If the usb device attached is an external hdd or other storage device then this could impact on the PC starting up especially if your bios has an option for other devices at boot up. Disable option for other devices (if listed).
Make sure that the hdd is the first boot option and that it is also the boot priority (sometimes shown as two different options in the bios).
I'm a bit dubious with the 660 watts PSU especially for an I7 motherboard, 720 watts would have been preferred (in my opinion).
Your ram might be the cause of the error, what brand/speed/type?
Also, what video card brand/model?