I'm attempting an unusual but genuine hardware project: running a modern RTX 5090 in an ASUS P5W DH Deluxe system with a 64-bit Pentium 4 641, 8 GB of DDR2-800 memory, a 128 GB SATA SSD, and a 1250 W power supply. The goal is to explore and possibly benchmark this unusual hardware combination, not to build a practical gaming PC. The system can already run Windows 10 and Windows 11, and it works with an older GeForce 9500 GT. The 5090 is known to function, but installing it results in spinning fans with no display output and no POST. The motherboard BIOS has a PCIe slot power setting with Auto, Low, Medium, and High options, though I haven't changed it yet. Could firmware compatibility, PCIe link speed, or another BIOS setting be preventing the card from initializing?
4 Answers
You could try booting with the 9500 GT first and checking whether the operating system can enumerate the 5090 after it loads, but that usually won’t help if the machine cannot initialize the card during POST. The operating system and drivers only matter after the motherboard has successfully handled the card’s firmware and PCIe setup. Even if you make it work, the Pentium 4 will be an extreme bottleneck; that’s fine for a unique hardware-combination project, but it won’t produce meaningful 5090 performance results.
It’s also worth testing the PCIe link configuration manually. Set the slot to the lowest available generation instead of Auto, and try the other physical slot if the board has one. Older chipsets can behave unpredictably when a modern card negotiates link speed or memory resources automatically. This is a useful experiment, but the age of the board still makes firmware support the stronger suspect.
The older 9500 GT working proves the basic slot and motherboard are functional, but it doesn’t prove compatibility with a current graphics card. Check whether the 5090 has a legacy-compatible VBIOS or a switch for a secondary firmware mode, and look for any motherboard BIOS update that improves PCIe or large-address-space support. Be careful with the slot power setting and change only one option at a time, since excessive voltage or power settings could damage the board or card.
The most likely issue is firmware compatibility rather than raw PCIe compatibility. Very old boards initialize graphics cards through legacy video Option ROMs, while newer cards may expect UEFI initialization. If the 5090’s VBIOS does not provide a legacy path, the system can power the card and spin its fans but still fail before displaying anything. A BIOS update or a card with legacy/CSM support would be the realistic fixes; changing slot power probably won’t solve a missing firmware interface.
That makes sense. The board is definitely using a traditional BIOS, so the card may never get far enough to negotiate a display output.
Exactly—the point is the absurd combination itself, not getting useful performance from the 5090. I’m mainly trying to make the system recognize it at all.