|You didn't answer all my questions & without that info, all I can do is guess. Please post the make/model of your motherboard, the make/model of your CPU & the make/model of your RAM.|
I can only guess that you have a 2.66GHz Pentium 4 which runs at 533MHz FSB. If I'm right, then DDR333 is the correct RAM to pair up with it. However, DDR RAM that conforms to the JEDEC standard is supposed to run at 2.5v, not 2.65v. JEDEC = Joint Electron Devices Engineering Council, they're the ones that set the industry standards. If you're not entering the BIOS & setting the memory voltage at 2.65v, it's very possible that the motherboard is assuming 2.5v is the correct voltage, in which case the RAM is being undervolted.
Maybe this will help explain: