Because you have replaced the CMOS battery the BOIS settings have been reset. The diskette drive error is probable referring to a non-existent floppy drive, so you will need to disable the floppy in the BIOS. Not sure about the CPU has changed gain it will be a BIOS problem but a minor one.
What is your make/model of motherboard? and I'll see if I can have a look at the user manual.