Third method - Channels.
Go back to your original image.
Go to the Channels pallet, here you should be able to see four selections. From the top they should read RGB, Red, Green and Blue.
By selecting one individual channel you are discarding the information from the other two, which should make your picture turn to B&W but make it look different depending on the channel you have selected. The amount of difference will vary quite a lot depending on your original image. Below I have shown the three versions I get by selecting each channel.
Red
Green
Blue
You should try each channel and decide which gives you the results that you most like, for this picture I chose the red channel but once you have decided go to Image > Mode > Greyscale, again Photoshop will ask you if it is O.K to discard the other channels. Select O.K and you are finished.