|I don't know what you have so I can only make some assumptions:|
1. your 2500+ has an unlocked multiplier
2. your BIOS has reset (weak CMOS battery?)
If that is correct, the CPU settings have dropped to 6 x 100MHz when they should be 11 x 166MHz (1833MHz). The 1st thing you'll have to do is replace the battery.
For best performance, the RAM should run at the same frequency as the CPU, so even if you have DDR400, it should be clocked down to 166MHz (DDR333) to match the CPU. The best RAM timings for nF2 boards is 2.5-3-3-11 & if you have the option to change the command rate, try 1T rather than 2T. Lock the AGP bus at 67MHz & always disable all Spread Spectrum options.
If the CPU multiplier is indeed unlocked & you have DDR400 RAM, you might wanna consider overclocking or at least reconfiguring the CPU settings to take full advantage of the board/RAM's potential. For instance, clock the CPU at 9.5 x 200MHz (1900MHz) with the RAM at 200MHz (DDR400)...that would be a mild CPU overclock but the entire system would benefit from the faster FSB.