While it is booting try hitting the DEL key (Pre-built systems from major manufacturers may use a function key such as F1, F2, or F10.), once the BIOS is loaded, go to the last tab or page of your BIOS. Select an option similar to "restore factory settings". Save your changes and confirm your selection if necessary. This will often be combined with the process of exiting a BIOS. Some BIOS types may have this as a separate option such as "F10: Save Changes".