Unknown Device

[mtm]

if it still cannot work, you can try to uninstall the driver usb(in your computer, maybe it's crashed in your computer).. and then install it again..

[sabxine]

thanks guys but non of them above works for me!
I also refresh my windows but nothing happens
I'll try to write the whole problem:
first of all when I connect the phone to the pc in phone screen always the usb connection menu pops up but when I choose one of the items:
sometimes the pc recognize phone as unknown device and often nothing happens in pc
and when it recognize it as unknown device none of the drivers of usb mach for this unknown device!!!!
but I dot know something...I dont remember...but may be I disconnwect phone when it connects to computer inn filetransfer mode or phone mode in middle of some proccess just may be!!!if I did a foolish thing like this is that what makes the trouble!but i should say i dont mean in middle of copying maybe just the windows of phone files open(the drive lette window waqs open) or in phone mode maybe it connects to pohoneexplo and i disconnect the phone without pressing F1....can this make the problem???and something else the phone works well with bluetooth...
thanks guys...