There are some filters that doesn't work on 64 Bits,try this :
- Go to Image -> mode and verifiy that the image is opened in 8bits/channel mode (like advised by CurtY).
- If it doesn't work,try to launch 32bits version (both are installed on your machine) and test it
Many thanks for those who kindly gave me suggestions. However none of them worked. And the real culprit seemed a 3d filter that is installed by default. Once I got rid of that particular filter, it worked fine. Once again I appreciate your helpful advices.
Normally that 3D Engine filter shouldn't cause those kind of problems.
If you want to get photoshop working properly some more information is needed.
(put the 3d engine plugin back in before doing any of the below)
Did you try resetting the photoshop cs5 preferences?
Have you updated your graphics card drivers from the gpu makers site (not through windows update)?
Could you post your photoshop cs5 system info as PECoutrtejoie requested?
(from withing photoshop cs5: Help>System Info)