visual studio 2008 is freezing in design mode

[tosbaqa]

It 's so weird issue :My visual studio hang up ,consuming 25% CPU and then I have to use the task manager to shut it down.This happened when i try to view the \[code\].aspx\[/code\] of the master page in the \[code\]Design view\[/code\] .After several attempts :I has found that removing some references to \[code\]css\[/code\] files fix the problem !!!! ..But i want to use those \[code\]css\[/code\] files .I wanna to know how some css files could freeze my visual studio !! ,and how to fix this problem .