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#11
Did you check that the CPU fan is running alright after whatever repairs/replacement you did?
Why did you remove the CMOS battery? Any specific reason?
Double check that you have replaced the CMOS battery properly as suggested by alphanumeric. ( I would suggest that you replace the battery with a new one - does not cost much)
Whatever connections you pulled out while opening the laptop to repair/replace the fan, make sure that you have plugged those in again properly - especially the connections to the laptop screen.