Plugging two cables into the same screen at the same time would not cause your problem to form. Your motherboard would have given priority to one or the other, and in addition your screen would have only displayed output from one or the other, unless you have a monitor or TV that supports picture-in-picture.
In all possibility (as much as I can gather from the confusing nature of what you are reporting) you have a failed hard drive. Try unplugging your hard drive, setting bios to boot from the optical drive, and then reboot with a Windows CD or bootable CD in the drive. If the computer boots the CD, it likely indicates either a motherboard level conflict with your hard drive, or a failed hard drive.
Another thing to check would be...