Dell Optiplex 3010 SFF wont POST (suggestions?)

[Nobody Important]

TLDR: Dell Optiplex 3010 SFF wont POST, tried googling for tips, none have worked so far. What else can I try?

What I have tried (as suggested on various other forum's when googling):

1. Removing 1 of the 2 installed DIMMs and trying using slot 1 only, then slot 2 only. Tried with 2 different sticks of RAM.
2. Changing the CMOS battery.
3. Resetting the CMOS using the CMOSCLR1 jumper
4. Changing the processor
5. Unplugging the front power button cable
6. Using HDMI instead of VGA (in case it's a display issue and not a motherboard issue)

Details:

I was given an Optiplex 3010 SFF (stated no processor, RAM, HDD - but working) as a freebie.

I obtained a working i3 2120 processor, and am reusing an old HDD I have as well as RAM. Lo and behold when I removed the cooler from the Optiplex I see that it does indeed have a processor installed (i3 3220).

It also had 2GB ram, which I removed and replaced with 2x 4GB sticks.

Re-using a 250GB HDD I had laying around.

I had to rewire the system fan as the cable was cut at the jumper (followed the same pattern as was before so not issue with crossed wires)

Plugged in the monitor and power cable, CPU fan comes on, motherboard light comes on (receiving power) but no display. At first I suspected perhaps the VGA port is not working so I tried the HDMI port, no change. Then I did some googling and tried the steps I mentioned above with no luck.

Does anybody have any suggestions on what I can try?

 

[WAslayer]

Determine whether MB may be gone.. to do so:

- remove all RAM and other non-essentials like hard disk drives and system fans (obviously not the CPU fan) and then attempt to boot.. you should hear beeping, provided there is a system speaker installed.. if there is beeping, motherboard should be okay..

If there is no beeping, swap to the other CPU and power on again.. if beeping, should be okay.. if no beeping, bum board/CPUs..

Also, make sure the CPU 4pin power connector is installed...