@PELC3530 

HDD is likely bad. Time to reinstall using OEM windows 10 DVD

Windows 7 is no longer supported.

If your 3020 is new enough it wont ask for a key because the 8.x key in bios will work fine for windows 10.

First test is to disconnect the sata data cable from Hdd and turn on

there should be an error on the screen.

Win10  Recovery DVD

Seagate 2TB 3.5 Drive

FFIDECO Dock for data recovery

Drivers for WIN10 come in a single CAB file.

http://downloads.dell.com/FOLDER04906888M/1/3020-WIN10-A03-D46TR.CAB

The driver cab file should be moved to the my documents folder.

Then extracted there using 7zip

https://www.7-zip.org/download.html

Then open device manager and say update my drivers from this pc instead of the internet.

Re:  no signal was going to the monitor nor was there any indication the HDD was running or win7 was loading. 

try clear cmos settings by jumper reset on motherboard.  first thing to rule out is corrupted cmos that is maintained by the new battery.  thus clear it to see if pc can POST.  currently you have a No POST pc so it does not even get to the stage of booting OS of hdd.  hdd is out of the equation now.

• Follow the procedures in Before Working Inside Your Computer .
• Identify the CMOS jumper (#5 RTCRST reset jump) on the system board, see the System Board Components.
• Place the 2-pin jumper plug on pins 1 and 2 to clear CMOS.
• 

   

https://www.dell.com/support/manuals/us/en/04/optiplex-3020-desktop/opt3020mtom/clearing-cmos?guid=guid-14c5b26d-ec68-4b01-aec4-8ec7ec251808

We have a problem, Houston.

Clearing CMOS

Check out How to Perform a BIOS or CMOS Reset and Clear the NVRAM on Dell Systems 

#5 does say remove jumper.

Also, simply replacing the battery resets CMOS.  However, if things aren't going right, redxps630 will suggest the jumper reset also.

What happens if you turn it on without the battery installed?

Did you try a different monitor?

And...Are you able to access BIOS?

If you try to access BIOS, remember to repeatedly press F2 right away upon powering on.  Don't wait for Dell logo or keyboard light.  You may need to restore default settings, also in the above link.

One more test:  Dell BIST Test  Remember, this isn't to see if your PSU is good, it's using the test button to see if internal peripherals are good with all external peripherals disconnected.

Your #5 must be different from the highlighted #5 above.

"Place the 2-pin jumper plug on pins 1 and 2 to clear CMOS"

I've pulled the HDD and reset the cables on it and the MOBO. I'll check it out a little later today. The monitor works quite well with another 3020. If the HDD has , which I find interesting as it's a WD Black, I have one or two at home I can try.

Sounds good.

It looks like redxps630 took the steps from the manual.  My #5 reference is from the Dell site link I posted.  Possible typo in the manual if it's not making sense.

Also, good luck in getting the 3020 going again.

Dearly beloved. We are gather here this day to bid farewell to our faithful and loyal servant JS2VG02. Opti, as he was affectionately known, passed on to the great IT Room in the sky on 15 Sept 2021 after faithfully serving his colleagues for over 7 years.

I have a spare HDD at home that I'm going to see if that will get this unit to boot. We also have a couple other PCs I can try to cannibalise but their HDD are just as old if not older. One of them was only used for a couple hours each week so it may be the better choice as well as being a Dell Optiplex 9030 (I think).

The Dell manual is buggy and might be auto populated by a bot.  I got a better pic than Dell manual, which shows a clear pic of the CMOS pin (IRTCRST).  Normally the pins are not jumped.  to clear CMOS you move a jumper from password pins (PSWD) to the CMOS pins for 5 sec, then move jumper back on password pins.

RTCRST

PSWD

I pulled the WD Black drive and installed an even older (ca 2009) Hitachi drive. The HDD activity light flashed like cop's roof bar. No video came out. I was using the VGA port. Yup, she'sa dead.

Right. I did an in place upgrade of an Optiplex 9020 tower to win10. Used CCleaner to clean up the hard drive. Since Dell still didn't believe in HDMI ports when this critter was made, I slipped in a DP to HDMI adapter. Plugged everything in and - VOILA! - I had a signal to the Samsung LED set. I does seem odd that both 3020 boxes' video died. Both were on win10 w\8GB RAM.

We'd rather not scrap out the two boxes, so any suggestions as to whether or not a SMALL HDMI graphics card would revive them?