Have you tried a different keyboard and mouse? It's possible that one of those are causing the USB ports to reset.
You can also try to do a system restore to a time prior to the point you started having problems.
So my USB ports have been intermittently failing, at entirely random times for lengths of time that vary as well. For as short as 15 seconds all my USB connections (i only have Keyboard and mouse in currently) will cut out and i will hear the windows ding that indicates connecting/disconnecting a device, sometimes the disconnect lasts for minutes at a time. It has been happening for a while so i thought maybe it was my MOBO going bad... so i changed to a new one. However the problem has persisted. Most recently i put in a PCI USB card, to try and remedy it and it still hasnt changed anything. Im not great with computers and am completely at a loss for what to do next. i REALLY don't want to take it to a professional and spend god knows how much on what could be just a loose connection or something. Does anyone have any ideas??
i5 2500k intel
8 gb ram
AMD Radeon 6800
ASRock Z75 Pro
SSD (cant recall manufacturer) +1 TB HD (same)
Windows 7 64bit pro
USB PCI (cant recall manufacturer)