The Collections are stored in the LR Catalog. If you had copied over your Catalog from the other computer to the new one all your collections would of been there.
Now that you have the images on the new computer, "IF", they were placed in the same folder structure (IE Same folder names and locations) then copying over the original Catalog "Should" include your collections. If they are in different folder names or on a different drive letter or drive name then you might be able to to use the Locate Images feature to find them.