CPU Fan Loud After Applying Thermal Paste – No Boot, No USB Power

After reapplying thermal paste to my CPU, I encountered a critical issue. The fan began spinning at full speed with a loud noise, and the system refused to boot — no display output, no power to the keyboard or mouse, and no POST beeps.

Here’s a breakdown of the steps I took and what could be causing this issue:

⚙️ What I Did:

• Removed the CPU cooler.
• Cleaned the old thermal paste using 90% isopropyl alcohol.
• Applied a pea-sized amount of new thermal paste (brand: Paste T).
• Reinstalled the cooler.

❌ Symptoms After Applying Paste:

• CPU fan spins loud and fast.
• No display output.
• Keyboard and mouse unresponsive (no LEDs).
• No BIOS/POST beep or signal.
• System doesn’t shut off unless I force it via the PSU.

🧪 Diagnosis Checklist:

1. CPU not seated properly – possible misalignment or bent pins.
2. Too much thermal paste – could be causing a short.
3. Paste spill – checked for excess paste reaching CPU socket or motherboard traces.
4. Disconnected cables – double-checked CPU power and fan headers.
5. Dead motherboard or PSU issue – not ruled out.

🔁 Fix Plan:

• Remove the CPU again and inspect pins (especially on AMD chips).
• Clean off the paste and reapply a smaller amount.
• Boot the system with minimal hardware (CPU, one RAM stick, no drives).
• Reset CMOS.
• Try booting the motherboard outside the case (in case of grounding issue).

🧘‍♂️ Lessons:

Always double-check your thermal paste application and CPU seating. A small mistake can simulate a dead motherboard or PSU.

💡 Tip for Others: If your fan spins loud but you get no POST, your CPU may not be detected. Don’t panic — start with the basics and test one component at a time.