My macbook pro does not turn off

Hi all,

My macbook pro (10.5.8) have been odd last week. When I try to turn off clicking in the apple symbol, it will close all my programs, hide the dock but then it freezes on the desktop image, without turning off. Then, the only way it turn off is pressing the on/off button in the keyboard. In addition, after i use for while (say 2h) it start to slowing down, performing some odd freezing when I typing in word or firefox.

I tried to reset Mac's PRAM and NVRAM and I use the Disk Utility to repair permissions, but i cannot fix for of them:

Warning: SUID file "System/Library/PrivateFrameworks/DiskManagement.framework/Versions/A/Resources /DiskManagementTool" has been modified and will not be repaired.
Warning: SUID file "System/Library/PrivateFrameworks/DesktopServicesPriv.framework/Versions/A/Reso urces/Locum" has been modified and will not be repaired.
Warning: SUID file "usr/sbin/pppd" has been modified and will not be repaired.
Warning: SUID file "usr/sbin/vpnd" has been modified and will not be repaired.

Could someone help me out?

I would appreciate any help.
Thank you very much,

P.