Overclocking?

hi i need some help with my over clocking currently i run a 2.2GHz amd sempron and i know ur gonna say dont overclock unless you can afford a new processor but i can. its just that i cant buy a new system cuz then thats a new mobo,new ram,newprocessor new gfx card yeah and that adds up so anyways.

i was just wondering how come when i go into my bios it says 200 mhz okay thats fine but when i try to make it faster like 250mhz the computer doesnt even boot… whats up with this. like the bios doesnt even load. so then i have to put jumpers on the mobo make the mhz like 100 then reset to deufalts and then take the jumpers off again back to 200mhz.
so is there a way to get it faster. because my cpu isnt nearly hot as it can go its usally around 42c-50c maxium and my proessor company says its maxium tempature is 90c so im thinking id like to go up to at least the high 60s. also im getting a new fan which is 10,000 rpms instead of my 3000rpm so it will be alot cooler. so i was just wondering why wont it go higher? some help please