Hello
The double boot thing is normal. What is happening is you have made changes to the bios, these changes need to be trained to the bios. What that means is the hardware has had setting altered that need to be tested to see if they work. This is the training.
When ever you power your system down and remove the power then the system has to retain your bios once again.
To set your system back at defaults it is easy. You can do two things. One is select F5 in bios and enter to restore defaults or simply clear the CMOS using the button at the back.
To help us help you - please provide as much information about your system and the problem as possible.