Overclocking problems

[Gbaby1008]

I've recently started to overclock my xp3000 333mhz its stock is 2.16 at 166. The farthest i can go is 160fsb-2.35. If i increase anymore my computer wont start up sometime the screen will stay black some times its loading windows and just reboots. Since i'm a noob at OC i'm guessing that it has to do somthing with voltages or sumin. I really dont understand it. Does it need to be higher and if it does how much?