1. If you are an Upgraded Member, you will have unlimited access to the themes. If you received your membership for free, you will have to save up 5000 points to access the themes.
2. If points were collected from your account and you cannot see it, then you may have chosen the "NONE" theme.
Under edit profile, specify again which theme you wish to have displayed on your profile by highlighting the corresponding bullet under the theme of your choice.
Be sure to then click Update Theme or your choice will not be saved!
3. Depending on your screen resolution you will see either more or less of the theme.
If you are running a standard 4:3 aspect ratio monitor (i.e. NOT widescreen), then you need to set your resolution to 1280x1024 before you see some of the theme. Anything less than that and you wont see the graphics but only a change to the background colour of your profile.
Generally you can change your screen resolution settings by right clicking on your desktop and select graphics or display settings and look for the resolution under one of the tabs or advanced setting buttons. This will vary depending on your Operating System. You can also try your control panel, and look for the Display icon, then go to the settings tab.
If this does not work, ask someone you are chatting with if they can see the theme on your profile. Most likely they will be able to even if you can't.