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Go to SolutionOptiplex 790 Dead after Processor Upgrade
When trying to upgrade an Optiplex 790 (Big, Hugest Available Tower) to an Intel i7-2600 Processor, the Computer continously runs all system fans, and the power button flashes amber along with 1 and 2 flashing LEDs on the front of the system. 3 and 4 do not illuminate.
When I unplug the power supply cable, the power button then flashes twice before no longer illuminating. 1 and 2 no longer illuminates.
I have removed the CMOS battery, reseat all RAM sticks, diagnosed with various sticks by switching slots and installing a different stick in DIMM Slot 1 and installed the previous Intel Core i5, yet I cannot get the system to pass POST.
I am an A+ Certified Technician, with Dell Proven Professional and amazed on what went wrong.
Unplugging the SSD and DVD Drive did not help, and I suspect a simple Processor upgrade has killed the system board.
I do not see a BIOS Jumper, but one may exist. Anyone have ideas?
Additionally, Dell has removed the Service Manual from their servers.
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Posted October 4th, 2026 13:14
Hi
I hesitated before posting my usual non-sense from the interweb, but soon got brave enough to do it...
If the old CPU also now produces the same fault, suspect a bent socket pin, disconnected power connector, damaged motherboard, or disturbed RAM.
If neither CPU works, do not keep repeatedly powering it on until the socket and power connections have been checked.
The 4 pin power sckt?
Kind Regards
anne_droid
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Posted October 4th, 2026 18:47
It's best to do the battery-removal, cmos-reset jumper, and remove all PCIe Addin cards (and use on-board video) ... all at same time.
If still bad, my guess is malfunctioning Intel i7-2600 CPU or bad motherboard. They do eventually fail sometimes. All it takes is one bad component, cracked via/run, or cold-solder on a pin.
Luckily (with a 3-digit model-number) it sounds old.
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Posted October 5th, 2026 03:00
@anne_droid "The 4 pin power sckt?" 2 flat prongs and if item is grounded, one additional pin here in the US. If you pull up an image of a US power cord or back of a PSU, you'll see what I mean. I think I know what you meant anyway.
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Posted October 5th, 2026 03:07
@ascendtek When you removed the CMOS battery, did you replace it with a new one (size 2032)? You might already know - bad batteries affect BIOS and PC operation.
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Posted October 5th, 2026 10:27
What I meant was the 4 wire power supply to the main board, which not all main boards have I believe.
So yet again I am omelette fizzog (egg on my face).omelette fizzog
(edited)
Kind Regards
anne_droid
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Posted October 5th, 2026 14:03
Hello everyone, I appreciate the replies and agree that they all can help in various cases.
It turns out I unknowingly bent one single pin on the LGA socket, and was able to get the system to POST with the i7 after alignment.
Thanks!
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Posted October 6th, 2026 02:59
@ascendtek Glad you got it working.
@anne_droid Now I see what you mean though I can't see your image. The 790 has 4-pin + 24-pin connectors.
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DELL-ChrisM2
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Posted October 4th, 2026 12:13
OptiPlex 790 Mini-Tower Owner's Manual
This link shows us that the blue jumper should be next to the four SATA ports.
#IWork4Dell
