Unless you backed up your iTunes library from the old computer and then copied it to the new computer, your iTunes library is gone now and you have to start all over again.
I'm not sure what you mean about when you entered iCloud, iTunes isn't available. You will need to explain that a little better. iCloud allows you to download the music again to your computer or to your iPad as long as you use the same Apple ID that you used to purchase the music or any other iTunes content.
Since you have a new computer and no longer have the iTunes library - or so it seems from what you are saying - you need to make the new computer your syncing computer. You might want to take a look at both of these user tips to see how you can do that.