Usb Keyboard Not Detected?

my usb keyboard works fine on my freind pc win7ultimate32bit, i have same os service pack 1 also installed, my usb is amkette company---better than local, Problemis that it was working grt for 5 months, but for past 3 weeks it is detected as a unknown device, it is detected sometimes as hid device and works well for 3-4 hoursbut then suddenly goes off and a popup with malfunction and unknown device appers all time, then it will never that day maybe 10 min sometime. i plug out all power cables,uninstall usb controllers tried everything on internet, some techniques work but no permanent solution. i even reinstalled windows last week no luck.It works on my freind pc., diff in my freind pc is he has intel motherboard and i have biostar a785ge everything up to date,only solution that is left is to use a ps/2 to usb convertor(i have to wait for 3 weeks).