https://www.dell.com/support/article/en-us/sln284978/a-reference-guide-to-the-dell-optiplex-diagnostic-indicators?lang=en

This system is over 9 years old and therefore should be replaced.

There are no soft fixes for physically bad hardware.

https://www.lambroinc.com/desktops?lightbox=dataItem-k5sk5m2k

Diagnostic LEDs for the OptiPlex series (2009 to 2012)

why not ask for help first and not change so many things OMG the CPU wHY DO THAT? and risk binding pins as 99% do and now mobo is no good

step one on all  PC this old is a new RTC coin cell.

below 2.9vdc the NVRAM scrambles and bios goes nutz, Chaos, never try to diagnose CHAOS or you go mad.

step 2 is testing, the HDD with SMART tests. no errors allowed.

step 3 new BIOS, newest.

set the BIOS PXE to OFF and not allowing it in the boot order,,set boot order to say USB then HDD0

safe boot off is seen,

USB ports enabled.

not fresh load the OS,  in legacy mode is best on old PC.

 loading any OS to a  bad HDD, (Run F12, ePSA diagnostics) will never run right the hdd must be good.

I have already cleared the CMOS. Would never boot.

Did you even read what I wrote? When I got the computer, the motherboard in it had bent pins. I bought a new to me board. So since the new board does the exact same things as the other, I thought it would be the CPU since those were the codes I was getting. Unless you are going to give support, don't reply to the thread, because you obviously did not read anything I put besides replacing the board and CPU.

• I bought a book about upgrading pcs and it specifically says that you should never upgrade more than one thing at a time. Make sure it boots after each thing you change so if it doesn’t boot, you know the last thing you changed is the problem.