hello all need help

my arduino ide suddenly cannot detect my arduino uno serail port...before this there was no problem at all can some ony help me.. im using windows 7 64bit

Try a different cable, does it work on a different computer?

on the other pc it working....

you say: "before this" but you dont say what "this" is?!? so we cant help you... need more information before what, so maybe we can help you.

Does the arduino switch on? If so: You might have to change the COM port setting on the arduino Ide, sometimes the setting changes.