I tried overclocking my brothers computer so i just put the FSB from 100 to 135 but now when i turn the computer on the monitor wont come on, the light is just flashing also, no optical mouse light comes on neither do any keyboard lights and the HDD light at the frot is constantly flashing.

What can i do to sort this out?

Turn off the computer and unplug it from the mains.

Open the case and take out the cmos battery for a few minutes. Replace the cmos battery, this will reset the bios to the default settings. Hopefully the computer should boot ok. You may need to enter the bios in order to reset some things after.

Regards Howard

If you didn't increase the voltage, you shouldn't need to worry about it too much.