PC won't boot after installing new RAM — memory training stuck

You just installed two fresh sticks of DDR5-6000 kit (say, G.Skill Trident Z5) into a Z790 board with an i7-13700K. You press power. Fans spin. RGB lights up. But the monitor stays black, and the motherboard's DRAM debug LED glows solid amber. No POST, no beeps, nothing. You check the manual — DRAM LED means memory issue. You reinstall the old RAM and it boots fine. What's happening here is not a dead stick. It's memory training gone long.

Why new RAM makes the PC hang

Modern DDR4 and especially DDR5 boards run a calibration process called memory training the first time (or after any hardware change). The CPU and motherboard talk to the RAM, test timings, voltages, and signal integrity, then store the working profile. On first boot with new RAM, this can take 30 seconds to 2 minutes. But if it doesn't complete — if it times out or hits a signal error — the board hangs indefinitely, the DRAM LED stays on, and you're stuck.

The real culprit is usually one of three things: improperly seated RAM (the most common), a BIOS that needs a specific timing tweak, or the board's training algorithm that just needs more time. Some boards, especially ASUS and MSI Z690/Z790, are notorious for failing training on first boot with higher-speed DDR5 kits — they'll hang for 5 minutes then eventually boot, but most people give up after 30 seconds.

The fix — three things to try, in order

1. Wait longer (5 minutes, not 30 seconds)

This sounds stupid, but it's the fix maybe 40% of the time. After pressing power, walk away for a full 5 minutes. Watch the DRAM LED — if it flickers or changes shade, training is in progress. Some ASUS boards silently train for up to 3 minutes for DDR5-6400. If after 5 minutes you still have a solid LED and no display, move to step 2.

2. Reseat the RAM — and push harder than you think

What's actually happening here is that one stick isn't fully inserted. DDR5 slots are tight, and the clip might click even when the stick is 1mm off. Remove both sticks. Inspect the slot for dust or bent pins (rare, but check). Insert stick A in slot A2 (second from CPU). Press down firmly on both ends until both clips snap in — you should hear two distinct clicks, not one. Repeat for stick B in slot B2. Reboot. If it still hangs, try one stick only in slot A2. Boot with single stick. If that works, the other stick might be dead or the board's slot B has an issue.

3. Clear CMOS — the reset hammer

This forces the board to forget any corrupted training data. Short the CMOS jumper (check your manual) or remove the coin battery for 1 minute. Some boards have a Clear CMOS button — press it with the PSU off. After clearing, try booting with one stick in A2. If it works, add the second stick after a successful boot. The board will re-train from scratch, and this time it should work because the corrupted profile is gone.

If it still fails — check these

• BIOS version: Older BIOS revisions on Z790 boards often have bugged memory training. Update to the latest BIOS using your old RAM first, then try the new kit. This fixes a lot of DDR5-6400 issues.
• RAM voltage or XMP: Some kits need 1.35V for XMP but boards default to 1.2V. If you can get into BIOS with one stick, manually set DRAM voltage to the kit's spec before installing both sticks.
• CPU cooler too tight: An overtightened cooler can bend the CPU socket pins slightly, causing intermittent contact on memory channels. Loosen the cooler bolts by a quarter turn each, then retry.
• Motherboard slot failure: If one stick works in A2 but not B2, and swapping sticks doesn't fix it, the B2 slot may have a bent pin or bad solder joint. That's an RMA.
• Memory channel population order: Most boards require sticks in slots A2 and B2 (the second and fourth from CPU) for dual-channel. Putting them in A1 and B1 can cause boot failures. Check your manual's recommended slots.

The core takeaway: that DRAM LED doesn't always mean your RAM is dead. Often it's just training being slow or a bad seat. Don't RMA the kit until you've waited 5 minutes, reseated firmly, and cleared CMOS. If you still get the LED, update the BIOS — that's the fix that catches the rest.