XP conflicting with bios?

I had just got a new computer, i had a guy i know order the parts for me, and put it together, i go in the bios, and set it at 1400 (processor is AMD Athlon XP 1600+) and load windows 98, no problems, and then i TRY to load winXP.. about 30 times or so, and it just will NOT load when its set at that speed, so i put it back down to 1050 which is my only other option, i finally get it loaded, so i go back in the bios, and set it back at 1400.. and it worked for a while, but then it just resets the computer after windows loads and gets to the desktop.. i don't know why it won't run at 1400 like its supposed to.. i formatted the hard drive about 30 times too, i did everything i could think of.