Do you know that a defective/faulty mouse can affect your windows and cmos settings? This is base on my experience having this kind of trouble. Specially for those who cant go to their cmos/bios settings. Don't suspect that it is your keyboard thats having a problem. If you are experiencing checksum error and done everything you have searched the internet.... (especially changing your battery, which is always what i have read) try unplugging just your mouse and try to use the keyboard only to enter setup... if this works, then the problem is your mouse. Try changing it to a new one. Hope this helps other people a lot.