Fan running 100% Lenovo M715q

Power down the system
Remove the power cord from power supply. (power cord from PSU to AC wall outlet)
Remove CMOS recovery jumper(#17 in image below - note its’ connection)
Remove CMOS battery (#24 in image below) (note the orientation of the battery)
Hold power button for 5 seconds
Reconnect the power cord to the AC wall outlet.
Power On computer and then hold Power again to Power off
Connect CMOS jumper back the way it was
Replace the CMOS battery back correctly
Power up (system may beep twice)
Press F1 for BIOS
Set the BIOS to the default settings
Set time and date
Press F10 to save BIOS settings and exit
Check if the fan is still running at 100% continually. If it still does you have a motherboard problem, possibly the temp sensor thinking that the CPU is overheating but it could be something else ;-)