Can i convert my compaq laptop celeron to dual core without changing th MB. Is it possible just by changing processor only

You'll have to look at the manufactures website for that model. Look for information on upgrades or techdata.

Although it's not likely. Most laptops are not made with anything upgradeable other than the hard drive and memory.

I will have to say that unless there is a motherboard that I have never heard of in your laptop it is not possible.
Intel Celeron processors are mostly in the 400-600 pin range and dual cores are in about the 700-1000 pin range. With a different number of pins the processors will not fit on the same motherboard. It's the same reason AMD and Intel processors cannot use the same motherboard.

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