Check the L1 bridges. They're on the top of the CPU, and are four little metal things. They either look like this :::: (locked), or like this |||| (unlocked). If they're locked, you can't change the multiplier. Get a pencil and draw across them, so that the graphite connects them and electricity can flow across them again. Be careful not to connect neighboring bridges, though.
Then, use either jumpers or the BIOS to change the multiplier (refer to your motherboard's manual).
If you can't get the multiplier to work, then overclock the FSB. You can change that in the BIOS (or through jumpers). Be careful though, since it overclocks your RAM, video card and anything in PCI slots, as well.
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9/11 - RIP</font color=green>