Short answer - clean your cache. restart your computer... that should resolve things.
Second Life uses hard drive space on your computer to store data, including a list of items in your inventory. If this cache becomes corrupted or your Viewer did not completely fetch your inventory, items in your inventory may erroneously appear to be missing. In many cases, your items are not lost and will reappear after you clear Second Life's cache:
Sometimes items get returned to the Lost & Found folder your Inventory. If you can't find an inventory item be sure to check there:
The Region you are in may be experiencing technical difficulties, especially in high traffic areas. This behavior can prevent you from rezzing items from your inventory. If you are unable to escape to another Region, exit Second Life and log back into a different Region:
Try to find a Region with a low Traffic score and relatively few objects- such Regions generally experience less strain, and are less likely to exhibit symptoms like inventory loss.
Sometimes it may appear that you have lost part of your inventory because outside forces can prevent Second Life from displaying your inventory properly. Remember: common solutions andsearch techniques can often solve a case of perceived inventory loss!
An unstable Internet connection can lead to apparent inventory loss in Second Life. High packet loss may cause your inventory to be unable to retrieve a complete list of items from Second Life’s servers. Wireless and satellite connections are unsupported for this reason, and other types of connectivity may yield similar results.
There may be a temporary problem with Second Life or your connection to the Internet. If the list of items in your Inventory usually loads without incident, temporary inventory loss may go away within 24 hours. In addition, clear your cache as described in Clearing Second Life's cache, logout and then log back in and look in your Inventory Window to see if the items have reappeared.
The Item Count in the Inventory Window is not always precise. It represents the number of items that have been successfully downloaded to your Viewer. Thus, if the number changes does not mean you have actually lost or gained inventory items. If you notice the number has dropped significantly and the Viewer has finished fetching your items then try Clearing Second Life's cache, logout and then log back in and look in your Inventory Window to see if the items have reappeared.