Don't worry, it's a popular problem at the moment, and there is also a simple solution for it

It seems I'm the only mentor reading this forum, we got that problem quite a lot lately with the new citizens and up to know the following steps helped every one of them:
- Click on "Edit" in the top of your window and move your mouse down to "Preferences".
- Once the Preferences window has opened, look for the "Network" tab down the left hand side and click on it.
- Once on the Network window find the button that says "Clear Cache" and click it.
- After you have clicked the button, log out and shut down your SL client and then re-open it on your computer, leave it for about 2 minutes after logging in and you should be back to normal and have a body again.
If you can see yourself, but have missing textures (white textures with the words "missing texture" written on it) then try the following:
- Go to debug mode by pressing CTRL ALT and D at the same time.
- Find "Client" menu on top.
- Scroll down to "Character"
- Click on "Rebake Textures"
Hope that helps!