PC Upgrade With New Memory and a Graphics Card Fails to POST
A small office PC with a micro-ATX board and a 300 W ATX PSU rated at 216 W on the +12 V rail is upgraded from 2 × 4 GB DDR4-2400 to a 2 × 8 GB DDR4-3200 kit. The board supports memory up to 2666 MT/s and lists slots A1 and B1 as the preferred pair. The user also adds a 75 W graphics card and removes the integrated-graphics output. After assembly, the fans spin, the power LED is on, there is no display and no beep; the keyboard Caps Lock does not respond. Refitting the old memory restores POST. The new 8 GB sticks are installed in A1 and B1 as the manual shows; one new stick alone in A1 also fails, while an old stick works in the same slot. The PSU is six years old. The user wants to return the memory as defective and buy a 500 W PSU.
1. Outline a logical POST-failure diagnostic sequence. Is the memory kit proven defective by the evidence given?
Read the worked answer
The evidence does not prove the memory kit is defective. The old memory works in the same slot, which shows the slot and basic board path are probably functional, but it does not prove both new sticks are faulty. The board may need a BIOS update for the new density or SPD profile, the new kit may not be on the supported list, or the CMOS may hold incompatible training data. A 3200 MT/s kit should downclock to 2666 on this board, but only if the board can train it.
Clear CMOS, load defaults, and test one new stick in the documented single-stick slot. Try the other new stick alone. Test the new sticks in a different slot and, if possible, in another known-good machine. Check the motherboard manual and BIOS release notes for 8 GB DIMM support, and inspect the CPU socket for bent pins. Remove the graphics card and use integrated graphics with a minimal configuration: one stick, CPU, one display output, no drives. Record beep codes or debug LEDs. Only after these tests should a warranty claim be made.
2. Estimate the power demand of the upgraded system and decide whether the existing 300 W PSU is the likely cause of the no-display symptom.
Read the worked answer
A rough load estimate is CPU about 65 W, graphics card 75 W, motherboard, memory, SSD and fans about 30–50 W, giving roughly 170–190 W total. The PSU's +12 V rating of 216 W is above that estimate, so the unit is not obviously overloaded on paper. However, it is six years old, its capacitors may have aged, and the graphics card may place transient demands on the +12 V rail. The PSU should be tested with a known-good unit or a proper load tester.
The no-display symptom is not best explained by PSU capacity alone because the fans spin and the old memory restores POST. A power problem would more often cause shutdowns, resets or no power at all. Check that the graphics card's auxiliary power connector, if any, is connected, that the monitor is on the correct input, and that the card is fully seated. Try the old memory with the new graphics card to separate memory compatibility from graphics installation.
3. What should you tell the customer, and what evidence would you record before authorising a memory return or a PSU replacement?
Read the worked answer
Explain that the new memory has not yet been proven faulty and that the existing PSU is probably adequate in wattage, although its age is a risk. Avoid selling a 500 W PSU as a guaranteed fix before testing. Offer a structured diagnostic: clear CMOS, update BIOS if appropriate, test each new stick alone in the correct slot, test the old memory with the new graphics card, and try a known-good PSU. If the new kit fails in another compatible machine and the old kit works in this one, a return is justified.
Record the exact model and serial numbers of the board, memory, graphics card and PSU; BIOS version; slot population; test results for each stick and slot; monitor and cable used; and any beep or debug-LED codes. Note the customer's approval for diagnostic time and any replacement parts. If a return is needed, provide the test evidence to the supplier. If the PSU is replaced, explain that it is a precaution or an upgrade, not a confirmed repair, unless testing proves otherwise.