blender is slow and unusable

i’ve used blender before and it worked fine ,
now i changed to ubuntu 64 bit (instead of 32) , and using blender is slow and lagging
that it can’t be used , i tried older versions 2.65 2.64 but it didn’t work , it’s like
the system is running smoothly ; applications and stuff , only blender is stuck , i
opened system monitor to see the usage of resources but all are normal even for blender ,
can somebody explain\help ???