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user_48c68a
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December 30th, 2025 04:58
Dell OptiPlex 790 Powers Off During Startup (Before BIOS)
I’m using a Dell OptiPlex 790 desktop. A few days ago, it started shutting down immediately when I power it on—either before or right after pressing F1. I suspected a CMOS battery issue and replaced it, but the problem persists. I also tried resetting/reinstalling, but the system powers off before I can even access the BIOS.
Has anyone experienced this issue or knows how I can fix it? Any help would be appreciated.
redxps630
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Posted December 31st, 2025 09:31
Try a bist of psu using Dell method. https://www.dell.com/support/kbdoc/en-us/000125179/how-to-run-a-power-supply-unit-self-test-on-a-dell-desktop-or-all-in-one-computer
make sure psu can deliver power to pc in a steady state.
next after replacing CMOs battery try clear CMOs settings via motherboard jumper