MSI P45 Neo (MS-7519 v1.0) doesn't boot Windows after upgrading from Core 2 Duo E4500 to Core 2 Quad Q9400

[tecnocamop1158a02dd]

Hello everyone.


I have an MSI P45 Neo (MS-7519) version 1.0 motherboard.
My hardware:
Motherboard: MSI P45 Neo (MS-7519) ver. 1.0 (Yes, pretty old board but i don't have anything else)

• Old CPU: Intel Core 2 Duo E4500
• New CPU: Intel Core 2 Quad Q9400 (SLB6B)
• PSU: FSP ATX-350PNR
• RAM: DDR2-800
• The system worked perfectly with the Core 2 Duo E4500.
• After installing the Core 2 Quad Q9400 I started having serious problems.
• Symptoms:
• The PC POSTs successfully.
• I can enter BIOS without any problems.

• CPU temperature is normal (around 40°C in BIOS).
• Windows Memory Diagnostic starts and runs.
• However, Windows never boots. As soon as the Windows logo appears, the PC immediately restarts.
• Safe Mode also causes an instant reboot.

I also noticed something strange:
With the Q9400 installed, BIOS reports the CPU running at 2.0 GHz (333 × 6) instead of the normal 2.66 GHz (333 × 8).

• Things I've already tried:

Cleared CMOS.
Reseated the CPU.
Cleaned the CPU contact pads with 96% isopropyl alcohol.
Applied new thermal paste.
Tested with only one RAM stick.
CPU temperatures are normal.
Windows Memory Diagnostic starts successfully.
The old Core 2 Duo E4500 still works normally.
Could this be:
an outdated BIOS that doesn't fully support the Q9400?
a damaged Q9400?
a motherboard compatibility issue?
something else?
Any advice would be greatly appreciated.
Thank you!