overclocking......

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,ive just been trying to overclock my pc bought just to try ,but failed.Ive read alot about overclocking but still a bit wary,if u know wat i mean.my spec is asus p5b 2180 cpu 2 gig corsair xms2 800mhz cl5 250 seagate hdd 7900gs nvidia trust 570 psu antec nine hundred case temps were 45 cpu and 35 mb till i got freezer 7 pro and the nine hundred case ,now there 33 cpu and 25 mb i was told all i needed to do with this set up was alter fsb ,which i did from 200 to 230 ...it failed so i tried 210 ,it worked but when restart it kept switching off then on then restart.would that be cause the pcie needs setting to 100 rather than auto?pls any info would be appreciated///i only want to get it to 2.5....