Your fan is probably close to dead. Fans do wear out which is bad, but cost 1-5€. Simply shut down & power off your box (since you can't boot it's in such a state already), remove the power cord (very important !) wait for 30 seconds and open the sheet metal.
Replace the fans by similar versions, if you have a computer shop near by, take te old ones with you. Don't be silly, change the CPU fan AND the power supply one, since you probably don't know which one is broken.
If you want to be more precise, go to the BIOS menu and do a fan test (if your BIOS supports it), another option is to try to start with the sheet metal removed, you will easily spot the one that stops turning.
Your fan is making this noise.
Fan speed is controlled by a sensor, and yours is no longer working, so it sounds as though the fan is running at full speed all the time, hence the loud noise.
Check the physical connection and clean the fan, but you probably need to have someone knowledgeable look at the situation.
hello, am annie and am having problems with my system fan 4 an hp g56. i accidentally deleted the cooling program from my control panel. now i got a message that my system fan isn't working properly. help.......