Was the Dell fan replaced with a non-Dell fan on those that require F1?   Dell fans have extra components on the fan and "report" to the BIOS.  A non-Dell fan will generate a "fan failure" and require manually pressing an F key to boot.  No way to get around it with a non-Dell fan.

On one of them, reseat the fan connector (with the PC powered off).  Then power on and see if it helps.  If not, do a CMOS memory (BIOS) reset.  But before you do the rest, note any customization you have in the BIOS as it will have to be re-entered after the reset.  To reset CMOS memory, with the PC powered off, remove the CR2032 coin cell battery on the motherboard for at least 10 minutes.  Reinstall the battery and power on and see if this fixes it.

If not it may be the fan electronics that the BIOS senses is bad and if that's the case, a new (Dell) fan will be needed.  If you have a working system that you can spare, take the fan out of that system and install (temporarily connect to one of the PC's that has the problem and see if fixes it.

Thanks for the reply and suggestions.

Those are on my to-do list but I thought I’d try ask if anyone might have seen this behaviour before and knew of a quick fix.

if I get chance, I will update the post with my findings.

There are no dell models in existence that allow you to BYPASS hardware failures and ignore them and boot.

no pc stated

no fan Dell Pn (DP/N#) stated.

did you check the RTC batteries first (less than 2.9vdc is bad battery )

did you buy a spare correct fan next , see it cures bad fans?  (they can be bad and spin too slow)

I changed both cpu and rear fans with noctua 4 pins fans. I unplugged the PWM signal pin from fans connectors. Both fans start and spin at full speed. No more bios alerts and  now I have satisfying silent cooling.

Hello, I have a problent with OptiPlex 7060, I installed win 10, but now it gives a No Boot Device Found error, update the Bios, but it doesn't work.

@Daniela Barrantes​ The easiest fix, which you may have tried already, is to be sure to enable all the drives in the bios and make sure it sees your drive. Dell BIOS allows you to enable and disable drives. If this fails, try a new cable, a new SATA port, if that's what you're using.

If you are using an M2 Stick you may have other issues. There are ways to manually build the boot sector, but let's not get ahead of ourselves here.

@Daniela Barrantes​ 

Starting your own thread would've been perfectly fine, as your subject is completely different from this thread.

What are you using for an HDD/SSD?

Try replacing the size 2032 battery and do a BIOS reset via the jumper method.  Bad batteries affects how BIOS sees drives.

Make sure BIOS stayed or is in the same mode the HDD/SSD was loaded in.  For example, if BIOS was set to AHCI when loading, it needs to be in AHCI now.