8500 oc problems

[*JEREMY*]

I bought an 8500 oem,its got the 3.6 mem chips and clocked at 249.8/249.8 default.The problem is that whenever I try to oc it by even 1 mhz the screen goes crazy with big color stripes.I have tried different tweaking progs and drivers and also tried it in win xp and 98.Anybody know what could be holding me back.The only thing I have not tried yet is dropping my fsb down but its only at 142 right now,think I will try dropping it now and see what happens

[moonman]

wierd, I have my radeon oem 250/500 at 295/610 rite now and running my cpu fsb at 153, it seems fine, try doing the volt mod it will help.