Do you have a different Dell AC adapter you can use to test the pc?

a bad adapter could do this.

cpu is almost never the issue of no POST.

does power button turn white or blue at all after the single amber blink?

unfortunately i don't have another 90 watt power adapter to try, i have a 60W but that doesn't work, the power button just stays off totally after the 1 blink, then a little while after i see the hard drive light blinking

Take it to a computer repair store such as Best Buy in US where they may have a Dell adapter to test the pc

hi i did that yesterday the same issue happens, any other suggestions?

1 blink is not in any Dell amber dx code

https://www.dell.com/support/kbdoc/en-us/000126021/a-reference-guide-to-the-dell-optiplex-diagnostic-indicators#2012_to_2020

(1) try RTC reset. https://www.dell.com/support/manuals/en-us/optiplex-5070-micro/opti5070_micro_sm/?guid=guid-f43ca142-3465-4f38-8fbe-2ad251ea73ff&lang=en-us

(2) check cpu socket pin since you swapped motherboard. Use a magnifying glass to look at the socket at 4 orthogonal angle closely after carefully extracting cpu. If you notice any bent pin, that is it.

Hi ok so i got a new motherboard and now it turns on but there is no video, no noticeable error codes either the light is normal white and doesn't blink or change to amber, i see some hard drive activity the keyboard and mouse shows signs of power , but don't get anything on the monitor

replace cmos battery of new mobo and clear its cmos settings (RTC reset).

I tried that but still no video, any other suggestions?

Re: i even bought a new motherboard

inspect mobo closely for bent pin

hi i checked there is no bent pins