Its the new hardware checks introduced in FW3.21.Same thing happened to me, 58% stuck in loop
DO NOT FORMAT YOUR HDD, I would recommend cloning that drive 1:1 so you can experiment with it but do not format without backing up or you have a brick. I read somewhere that it would get me out of loop if I formated drive and took out internal battery, I got an instant brick as the nand had already been semi flashed so the only thing keeping my ps3 looping was the bit of the firmware on hdd .
I was updating from 1.60 or 1.80 so I had no recovery menu not that I could get into it anyway even if I did. Ive read that If you can get a friends HDD thats on the firmware you was on,clone it,take out internal battery as there is a "Update flag" on both the HDD and the Bios(removing battery clears bios flag,using friends drive clears HDD flag), then put your cloned friends drive in it will not know it was in update mode/loop anymore and it will read the hard drive as corrupt because its not from your ps3 it will ask you to reinstall firmware that you was on, and you can install 3.15 again as it has not got the extra hardware checks.
Please do some research on this as there is lots of info out there on this update loop error , some say if you change the bluray drive to a working friends bluray drive as its updating but before it loops you can get past the loop but thats only if its bluray drive problem.AGAIN, very important DO NOT FORMAT YOUR HDD, THERE IS A UNBRICKING THREAD SAYING THIS WILL HELP BUT ALL IT DID IS COMPLETLY BRICK MY PS3.I have no hope of getting a friends HDD on same firmware as I was on because I was on really old firmware.
You could try a few experiments out if you manage to get your drive cloned such as unplugging bluray drive altogether to see if it loops at different percentage,try to trace hardware problem like that.maybe unplug wifi module and card reader if you have one.Some people who got stuck in this loop didnt realise thier was anything wrong with their ps3 but the firmware update picks up on some small error and just loops,completely sonys fault I think as internal hardware mods are not really a threat to them but that is excuse they use for new checks.
Worst thing is after I bricked my one I found small bit of damage on the bluray drive ribbon cable.If I had of done alot more research and not just followed first unbricking guide I found I probably could have saved it.For one I would have updated to 2.50 first so I had recovery menu
Originally Posted by GrandpaHomer
I could be wrong about this but Depending on stage it looped at I reckon the flash is probably not complete,if you put in a blank drive it will not have the bit of firmware that asks for the usb drive.
1. update downloads
2. update installs over to HDD
3. reboots and boots from the HDD files ,
4. erases and then flashes the Nand but must not sign itself until completes update.
spose you could try use a differnt blank HDD and see what happens?If you get black screen you will know how I felt
if it asks for firmware update file on USB see can you do a reinstall of 3.15 as hardware checks were not as strict on 3.15
edit: this bit is wrong ,it wont ask for firmware update,
Originally Posted by DeViL303
You should go straight into recovery mode as soon as ps3 boots with friends drive and select restore ps3 system, apparently the recovery menu is bootable even off someone elses drive,I might do some more experimenting with my brick!