blue Lines rectangle following cursor and all Applications and system freeze - snow leopard hello, i have a big problem with my macbook pro when snow leopard 10.6.8 startup, gray screen appers and freezes. what did i : 1 - i tried to boot from Install DVD but blue screen appears and freezes. 2- i booted from external HD in safe mode and i erased my HD by disk utility and i installed clean os from external HD ( in safe mode - blue lines around the cursor - see the picture) but the problem still, i booted in safe mode and i updated the os to 10.6.8, and the problem still, 3- i reset the SMC and PRAM and EFI. and same problem 4- i repaired the disk and permission from ( external HD - safe mode and from single user) , after that the system worked fine and no problems occurred, i startup snow leopard normally and every thing fine, but i tried to open any application - blue Lines rectangle following cursor and all Application freezes, but i can move the mouse. the problem sometimes happens and sometimes not. i opened disk utility and verified disk, the hard disk is ok i repaired the disk permission - the disk utility repaired many files successfully (every time i repair the disk permission, same files repaired but not working ) - i changed my RAM and HD - no results i tried to install lion os but my mac dual core, lion os mini Req. core 2 . - any help please?