Something like that happens to me in order to play oblivion I`ve got to
uppgrafe my processor from a sempron 2400+ to a athlon xp-mobile 2600+
mi crap mobo donīt detect the new procesor so I download CPUID from
Crystal Dew World site, beware it`s japanese so turn into english
http://crystalmark.info/?lang=en
execute and in the k7 utilities have a voltage and multiplier change
the numbers to your original settings It`s the easy option otherwise
you can open the case an change the fsb pin but Ive done it t first
place but with 166 fsb the agp slot got very hot and have artifacts the
radeon 9550 i have at overclock
I hope it helps you, greetings.