Hi! what you should do is to clear (reset) the c-mos. This is usually done by setting a jumper on the Mobo. One word of advise though, the computer must be shutdown (off) while you are doing this.
1. Make sure that the computer is powered down
2. Find the right jumper (look in your manual)
3. set it to "clear cmos"
4. set the jumper back in its original position
5. Power up.
Now you should be able to get into the BIOS, which by now has all its values set to "default". Make the optimum settings for each item, save and exit. If you still wan't to OC raise the FSB a couple of steps every time, i. e. from 133 to 135 and so on.
GL
Turk
PS you don't have to flash your bios, thats a completely different thing.