Hello there. I have had this problem with my cpu for some time now but ive come to the conclusion i have no idea how to solve it. I currently have a Socket A PCCHIPS M848ALU mobo with an AMD Athlon XP 2400+ processor. This is supposed to run at 2GHZ, however I cannot reach above 1.5ghz. I have considered upgrading my PSU, which is currently a quite old 350Watt one, running 2 case fans and my mobo (connected to which are 2 HDD's, a radeon 9600 pro, SBAudigy 2 Card..). I guessed this load may be too much for the PSU and might be grading my CPU performance.
I have also considered heat, but it runs idle at 45C, not ideal but not quite overheating.

I was wondering if anyone could help with a suggestion? Thanks very much for reading, and any responses are much appreciated! dont hesistate to ask further questions also.

Update: I have just checked under my system settings and the CPU is recognised as a 1800 Athlon XP. I know for a fact the CPU i purchased was a 2400, and apart from that it has run as a 2400 @ 2.0 GHZ before (when i first purchased it)

You have the FSB set at 100MHz (200FSB) instead of 133MHz (266FSB). If it's not a BIOS setting, there's probably a jumper or DIP switch on the board that has to be adjusted. Check your manual...or download a copy from the PCChips site

yeah, the cpu is meant to run at 15 x 133 = 2000mhz. I have a pc with that mobo and its in the bios that you set the fsb. If you set it to 133 and when it post's and still shows a 100fsb then the cmos battery may be low or the psu might not be strong enough.

if it was previously running at it's correct speed it sounds like the bios settings are getting lost when you either reboot or shut down and power it back up. If this is the case check out the voltages in the bios for the 3.3v, 5v and 12v rails and see if any are out of 5% tollerance.

Abit NF7-S 2.0
XP2500-M @ 11.5 x 204=2353MHz
Tt Volcano 7+
512MB DDR 1x2700, 1x3200
120GB Maxtor D9 8mb cache
GeForce4 Ti4200 @ 300/600