See This chart.

https://www.dell.com/support/article/us/en/04/sln284978/a-reference-guide-to-the-dell-optiplex-diagnostic-indicators?lang=en#2012_to_Present

do the long reset.? are all fans silent? that true?

or first push power for 5 full seconds, button ,cured now?  this what I call the intel reset (ICH chip sleep failing)

then the long reset is next.

then then, and lots more.

blinking amber means power failure, learn that the PC does not know why only that it IS.

the top cases are:

Coin cell dead

PSU see overloads in the PC, (we strip PCs to find what part is shorted) or the mobo strip.

or PSU is bad.

PC have what are called shared resources, if things short  boom dead. ever power rails inside shorted, even USB device ! dead shorted, (have proof of all)

if you wont take the lid off , find a shop to fix the PC, the line is long.

Note: On any OptiPlex built since 2012 , Dell has stopped using every beep code - except for the Memory Failure code (1,3,2 or 1 beep, then 3 beeps, then 2 beeps).

https://www.dell.com/support/article/us/en/04/sln284978/a-reference-guide-to-the-dell-optiplex-diagnostic-indicators?lang=en#2012_to_Present

Power Button LED Description