EDITED
Hi LittlegirlRosy,
Your Operating System is either 32bit or you have one of the Intel HD graphics cards which also limits you to the use of the 32bit viewer. Please completely uninstall the version of Second Life you are using, then download this version of Second Life and install it.
http://download.cloud.secondlife.com/Viewer_5/Second_Life_5_1_5_515811_i686_Setup.exe
If you are having any further issues please file a bug report at https://jira.secondlife.com and I will be happy to help you there.
Thanks!