Here's a tip for you. Watch how the computer wins this game. Set it to Level 4 and get the computer to play against himself. If you like you can print off the moves and play through the game yourself.

White: Human Black: Computer (king, rooks, bishops & pawns)

The chess engine on this website is p4wn, written by Douglas Bagnall. For further information please visit his website.
To use this program, click on the piece you want to move, then on the square you want to move to. If you want to castle make the king move and the computer will move the rook for you.
To play black click on 'swap'. To change levels click on 'computer level'. There are five levels: 0 is the easiest and 4 the hardest. To take back a move click on 'undo'.
To see the computer play itself click on 'white'. To get the computer to act as a referee click on 'black'. In either case the icon will toggle between 'human' and 'computer'.
If you want to promote to a piece other than a queen click on 'pawn becomes' until you see the piece you want.
If you find you can't play the move you want it's probably because you haven't noticed you're in check.