Shut up faiza, you and your alts never bother to read posts do you? Actually just take the time to read the part I quoted.
Sorry for misunderstanding but he is asking for help about bitcoin core software which have already his coins
He doesn't need the blockchain. He just needs the privkey of the pubkey which received the bitcoin, so he needs instructions either to dump his privkeys or convert wallet.dat into something usable by a light client (or maybe some natively can, now, but I'm unaware of them).
There are two methods I know of to do this:
1) Use Core command line to export privkeys.
http://bitcoin.stackexchange.com/questions/5324/how-do-i-import-private-keys-from-bitcoin-qt-to-multibit-client2) Use pywallet to extract the privkeys.
https://bitcointalk.org/index.php?topic=34028.0#1 includes a method to import the privkeys into MultiBit.