I recently picked up an Asus P4B266-C. It had some failing capacitors, which I replaced, and I was able to install Windows 98 SE with no issues after that. Though it is officially a 400 MHz FSB board, I saw posts on old forums that indicated that people had used 533 MHz FSB CPUs with no issue. It came with a 1.7 GHz chips with 256 L2, so any of the 533 chips I have would be an upgrade. I tried a couple of different Northwoods, a 2.4 and a 2.5, and wit hthe board in Jumperfree mode, the BIOS recognized them, and all seemed well. Except after you saved the CMOS settings and exited, it wouldn't POST. When you power cycled it, it would again boot stright into the BIOS settings with a warning that it failed to POST because of the "Incorrect" CPU settings, and was now in Safe Mode. Save it again and the same thing would happen. So I decided to try underclocking the chip by leaving the FSB at 100 instead of 133, but when I did that it would lock up in Windows every time. I tried updating to the last BIOS (which is a beta), I tried the next to the last BIOS, I tried different memory, etc., but nothing would work but the original 1.7 CPU.

So I decided that this board must not work with 533 FSB CPUs, and I bought a 2.4/400/512 chip for it (officially it supports up to a 2.2 GHz). When I installed it it went straight into the BIOS and it recognized it, then got into WIndows and locked up. I again tried all sorts of things. I switched from Jumperfree mode to standard mode, and this seemed to improve things; it would POST every single time, but now it would make it into Windows setup and eventually lock up. It once made it as far as "Copying files 77%" before locking up. I tried a different cooler, different video cards, different RAM, switching RAM slots, but nothing worked.

It seems as though something is heating up - the time I made it to "copying files 77%" I had let it sit and cool off for a while. The odd thing about that is that the 1.7 CPU that it works perfectly fine with has 1.725 core voltage where the other chips are around 1.5 volts. Maybe the higher CPU frequency is overheating the VRM MOSFETs and causing the lockup? Thanks for any ideas.