Test My Theory, I Dare You.

I believe the problem is System resource configuration. Lights (1) and (2) were the ones I seen. It says that some steps to come about a solutions might be. Reset the BIOS and clear the NVRAM and any previous errors, remove all external peripherals, If leds change, add parts back one at a time until fault re-occurs and contact your tech. My source is:

https://www.dell.com/support/article/us/en/19/sln284978/a-reference-guide-to-the-dell-optiplex-diagnostic-indicators?lang=en#2005_to_2009

-We have concluded that you needed to take the memory out and plug it back in, so someone probably accidentally knocked it loose