Saint is correct, this is normally caused by (1) low battery (2) corrupted bios (ie a bad flash). The "watch" batteries use in computers normally only last 3 to 5 years, but you never know as the battery could have been sitting on a self for an extended period of time. It was probably low, and when you wrote to the Bios (higher drain than just sitting there) you used the last of the juice. If replacing the battery does not fix the problem (will probably need to reset some bios values) then the problem is that the bios itself is infact corrupted.
And no the hardware changes should not have caused this, But you may need to verify some bios seting such as using the usb port for keyboard.