STEP 1;

Photoshop CS5 has new GPU-acceleration to help with 3D editing. Many graphics 
cards will probabely need their drivers updating to the lastes versions, 
others may not work at all. 

Use the link below to see the cards CS5 Photoshop was tested on before release.  

http://kb2.adobe.com/cps/831/cpsid_83117.html 

http://kb2.adobe.com/cps/404/kb404898.html

If the 3D menu is greyed out try turning on OpenGL drawing in the 
prefferences - performance menu.  

http://kb2.adobe.com/cps/840/cpsid_84020.html

STEP 2;

Start photoshop then wait 2 minutes then go to HELP then ACTIVATE if ACTIVATE
is greyed out then you are full activated and all features that your hardware
supports are enabled.

STEP 3;

Windows Vista & 7 users go to start menu and right click Photoshop CS5 and run 
as adminastrator, wait 2 minutes then restart Photoshop as a normal user.