iMac 27" A1419 820-3299 usb disabled at login page

[guruji]

hello
I have this weird machine that came with power issue fixed the power supply now the machine boots up but the USB ports don't work.For some strange reason if I press Option and boot from pen drive I can use the usb all ports work.there is something that disables the usb when comes to login page. I reprogrammed the bios same problem.the ssd in this machine has Catalina and when I go to boot with high Serria usb bootable it gives me a cross that os not compatible with the machine.only Yosemite usb bootable works.So is there some terminal command that disables the USB ports.is it that the firmware is old of the smc as it takes only Yosemite .my question how did the customer put Catalina maybe patcher but wireless keyboard works but not usb keyboard.
has anyone faced this usb issue getting dibbled at login page

[reformatt]

Most common issue I see with all iMacs these days are inline chokes for the USB ports are high resistance. Ports either don't work or are flaky. Should measure about 4 ohms resistance for each coil, any higher they are faulty. Part number is DLP0NSN900HL2L. Sometimes fault on Port 1 is U4610. You can steal these parts off a Macbook Air donor board as well.

Also make sure you do a PRAM reset. 2012 iMac should boot Catalina. Make sure the installer is a current one as the security certificates expired a few years back and all the installers had to be updated by Apple.