"Alert! Previous Fan Failure" Diagnosis & Repair Checklist
TECHSPOT forums have helped me with great tech advice in the past, so I am offering the following diagnostic procedure as my first post in these forums. It includes almost all of the recommendations made throughout this thread combined with some from my own experience with this problem as a technician. I did my best to give credit to those who posted great recommendations.
"Alert! Previous Fan Failure"
Diagnosis & Repair Checklist:
STEP 1: CHECK THE FAN. If the fan is dead, wobbling, smoking, or on fire, it must be replaced. Use compressed air to blow any dust out of the fan. LOOK CLOSELY and make sure the fan is connected to the appropriate power connector on the mainboard; often there are multiple power connectors for the CPU fan and CASE or SYS fans. Check that the entire assembly (fan, screws, heat sink, clips) is properly mounted in the retention bracket; the metal heat sink should be held firmly against the CPU with snugly fastened clips. If the assembly seems loose, it is either assembled improperly or it is broken. If you find any of the above to be true, skip to STEP 5.
STEP 2: ENTER THE CMOS/BIOS SETUP UTILITY. Getting there isn't always easy. Since the "Alert! Previous Fan Failure" problem is primarily specific to Dell computers, tapping on the F2 key after turning the computer on should get you into the BIOS/CMOS setup utility. If it doesn't, try the DEL key or some other F# keys, just be careful to not restore your computer. If the computer does not seem to be receiving your key strokes, make sure your keyboard is in good working order and properly connected to the computer (and not plugged into the green PS/2 mouse jack). If the setup utility asks for a password, enter it. If you do not know what the password is, look on the mainboard for a jumper that will reset the CMOS password; if you can't find a password reset jumper, GOOD LUCK. You could search the internet for CMOS/BIOS password removal tools and perhaps get lucky and feel like a hacker!
STEP 3: CHANGE THE CMOS/BIOS SETTINGS. Once you have successfully entered the CMOS/BIOS setup utility, you are in the home stretch. Clearing the event log seems to have been the #1 SOLUTION for a lot of people who posted here, which makes sense because the error message says "previous fan failure" and not "current fan failure". Changing the "DO NOT report keyboard errors" setting was the #2 SOLUTION which really does not make sense because the keyboard and fan operate at different voltages and are generally unrelated, HOWEVER! since it worked for them it might work for you. You can always try resetting the CMOS/BIOS settings to the "default" or "safe" settings, but you may notice your computer behaving differently afterwards, and it is therefore not recommended. It seems that all CMOS/BIOS setup utilities are a little awkward to navigate, so look for instructions on the bottom or right side of the screen if you are having trouble.
STEP 4: UPDATE THE BIOS. Hopefully the error message is gone. If not, there are a few more things to try. The reason why this procedure has a reputation is because every once in a while it quickly and unsuspectingly destroys people's computers! (actually, just their motherboards!). During the BIOS update process, if the procedure fails for any reason, the computer will no longer boot and the motherboard will be have to be replaced. With that in mind, go to Dell's support web site, enter the computer's model number or service tag, and download the most recent BIOS update (located in the device drivers section). Follow the instructions carefully and guard the power strip.
STEP 5: REPLACE THE FAN. If the error continues to appear, there may be a problem with the fan, its wires, or the connector. If you replace the fan, make sure it is the correct size (92mm fan is common with Dells as mentioned earlier by "benthere") with a power rating of 12 volts and around 0.42 amps (as mentioned earlier by "wsnett") which should draw about 5 watts. If you must remove the entire fan & heat sink assembly, be sure to clean up the old thermal compound residue using isopropyl alcohol and then apply new thermal compound; make sure the heat sink is seated and secured firmly against the CPU; make sure the clips are properly attached to the brackets; make sure the fan is plugged into the motherboard properly.
STEP 6: STILL HAVE THE ERROR? "snoopindaweb" posted this key sequence at power-up: turn on -> CAPS LOCK -> NUM LOCK -> SCROLL LOCK -> ALT+E -> ALT+B -> ALT+F, then do an "Automatic IDE Configuration". I haven't tried it because I didn't need to, as the list of recommendations above solved the problem.
STEP 7: BUILD A NEW COMPUTER. If you are frustrated and don't like the way Dell builds computers, and you feel the need to post unhelpful, angry comments in an online forum like TECHSPOT, then you must step away from the keyboard, gain control of yourself, take responsibility for your anger, and claim ownership of your computer by building one yourself. Its fun, educational, and impresses the opposite sex.
I enjoyed putting this together.
I really hope it helps someone.