Windows 7 - Usb keyboard not detected

hello,
please help me out of this frustration..
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).......if any technical solution is there plz help....i have many imp works to do on pc.....please helpanyone....each usb port work bcz usb mouse logitech works on each one......Help?/

Only additional thing I can think of is to check the pnp settings in the bios.
It also would not hurt to go to the power options in control panel
click change plan settings
click change advanced power settings
expand usb settings and make sure usb power suspend is disabled.

Try plugging a USB thumb drive into a slot during the keyboard problem. See if Windows will recognize the thumb drive or if it's ignored and/or the keyboard comes back. Some motherboards have a problem with sleep states and as Maguscreed says, your power saving settings may be set too aggressive.

Keyboards draw next to nothing in power so it's not likely it's heating up and failing. It's most likely the power settings.

I honestly don't even know why they bother with trying to manage usb power since it's dealing with about the same amount of power as a couple of 'aa' batteries to begin with.

Right, I second Maguscreed's suggestions. It may be a power problem.

Also, just how many USB devices do you have plugged in? Sometimes you can have just too many external devices like USB drives, keyboard/mouse, external hard drives, etc, and tax your power supply beyond its limits.

thanks guys i disabled selective suspend , actually kb was working for 3 hours that usually it does in a day , meanwhile i disablled that selective suspend under usb in power settings so i hope if it works.....permenanaently..STILL THANKS GUYS....Maguscreed, carwiz

thanks guys your advice still working seems a permanent solution u saved me a lot of time ... thanks...

I have a similar problem occasionally after start up. The keyboard does not work & device manager does not show any keyboard is present. On previous occasions I could fix it by restoring computer to a week earlier, and then right clicking on Human Interface Devices in Device Manager and making it search for the keyboard. When it showed up I updated the driver software.

Today, none of this worked but when I logged off and went to a different user, it worked! Then back to the original user and it worked again. What is going on??

this is generally caused by faulty hardware that can be cured by minor changes in system like power solution mentioned above by Maguscreed . or you can check if keyboard wire is ok , the point where wire enters the keyboard sometime streches you can try to push it in and fix by tape or smth else or usb port may be faulty in my case wire from keyboard was faulty i pushed it little inside keyboard and fixed with tape so that it dont move at entry point now its working