Why is this cpu not compatible with my motherboard?

I have a vpc2222 / rs-310 sony computer. It has a i845g chipset motherboard which is currently equipped with a 2.4ghz RK80532PE056512 pentium 4 processor. I inserted a 3.2ghz pentium 4 ( SL7PN) . the pc light blinks but it wont boot and nothing comes on screen. Why is this and which similar processor would work in my pc.