From Second Life Wiki
If you are unable to see your avatar, it could be due to any of several reasons, including your graphics card, drivers or internet connection.
Are you using two monitors?
At least on some computers(*), if you have two monitors and you rebake your av's texture when your SL window is not sitting in the primary (i.e. first) monitor, you will turn transparent. If this happens, just move the window back to your primary monitor and rebake again.
(*) Empirically, this appears to be a monitor/graphics card port issue rather than computer. Thus swapping which monitor is primary and which secondary will also help in some cases.
What graphics card are you using?
Click on the Help menu at the top of your screen, and select 'About Second Life'. In the window that opens, your graphics card type and manufacturer are listed about half way down.
Second Life supports medium to higher end nVidia and ATI cards. Support for Intel graphics (which is a chipset on the motherboard designed primarily for 2D graphics) is not available.
Are you using the latest graphic card drivers?
Even brand new PC's often ship with outdated graphics card drivers. It is highly
recommended you go to the site for your graphics card and download and install
the latest graphic card drivers.
Choose Me > Preferences to display the Preferences window. Click on the following tabs:
Graphics tab: Change Draw Distance from 128 down to 96.
- Under Avatar rendering, un-check Hardware skinning. If it is unavailable it means your graphics card does not support it.
- Under Mesh detail, make sure the Avatars slider is in the middle setting.
- Click Hardware
- Increase Texture Memory to the maximum available.
- Change the Maximum Bandwidth setting to a speed lower than your internet connection speed. Suggestions:
- 768 Kb: set to 400 kbps
- 1MB/s: set to 500 kbps
- 1.5MB/s or greater: set to 1000 kbps
- Increase Cache size to the maximum (1024 MB) .
In some cases check if you tryd to use OpenGL under the advanced graphics settings. Some cards dont support OpenGL any more for SL.
Clear your cache
See Clearing the cache. Be sure to log out of Second Life. Log back in.
No, all that didn't help!!! What now?
It's possible your firewall may be preventing transfer of some data - try disabling your firewall temporarily and relogging in to Second Life. Should that not assist, please contact our tech support department via support@secondlife. listing your system specifications, and the steps you have tried (as above) to correct the issue.