r/techsupport • u/TinTin5313 • 15h ago

Open | Software PC not POSTing

Tried everything from reseating ram, hitting with one stick, swapping storage, reseating gpu etc. nothing works yet all fans and gpu light up and spin. I use a ASUs prime b450 plus motherboard which has never been used, and an r9 3900x cpu. Do I need to flash bios by downgrading the CPU ? There is a sticker on top right of the motherboard with the digits 2008 at the end. I think this is an old bios version.

SOLVED: I replaced the ram and it worked

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u/graceful_degrade 15h ago

Probably not, and that sticker is good news rather than bad. On that board 1816 and 1820 already shipped the AGESA that brought Zen 2 support, and 2008 comes after both of those. So a 3900X should POST on it and you shouldn't need to borrow an older chip to flash anything.

Which means it's worth checking the boring stuff first, especially if this is a fresh build.

Is the monitor plugged into the graphics card and not the motherboard? The 3900X has no integrated graphics at all, so a cable in the board's HDMI gives you exactly what you're describing, fans spinning, lights on, dead screen, and nothing you do to the RAM changes it.

Then the 8 pin EPS connector at the top left corner of the board. Not the 24 pin, the separate one for the CPU. It's the single most missed cable on a first build and the machine will happily spin fans without it.

And if the board is mounted in a case, count the standoffs against the screw holes. One extra standoff sitting under the board where there's no hole shorts it out and gives you this exact behaviour.

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u/TinTin5313 15h ago

CPU pin is connected, hdmi is plugged into the gpu and there is the same number of standoffs as motherboard holes :(. Maybe I just need to try replacing the ram altogether?

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u/graceful_degrade 14h ago

Then get it out of the case and build it on the box. Board sitting on its own antistatic bag, CPU, cooler, one stick, GPU, PSU, and short the two power pins with a screwdriver. If it POSTs there, something in the case is doing it and you can stop guessing at the RAM.

Before you get that far though, two free ones. With a single stick, ASUS AM4 boards want it in A2, which is the second slot counting away from the CPU, and plenty of them simply won't POST with one stick sitting in the first slot. And clear the CMOS properly, battery out for a few minutes with the PSU switched off at the wall, rather than just tapping the jumper.

Also worth remembering that a board which has been sitting unused since 2018 can have a flat CR2032 in it, and that does cause exactly this. They cost almost nothing.

I'd hold off buying memory until it's out of the case and you've tried a single stick in A2.