Dell Inspiron USB ports (not all) not working

I have four ports. Two are working, and other other two are not. My Logitech unifier is recognized and also the cable to and my printer.

Flash drives are not at these two ports, but if I remove the unifier and plug in a drive, the drive is recognized.

I ran Dell's "USB Status Test" with the pre-installed software, and both "pass the test"

Device version 0.0.0
USB version 2.0.0
Microsoft driver version 6.1.7601.21692, 6-21-2006
Driver c:\windows\system32\drivers\usbhub.sys (more may be truncated??)

I ran the USB POrts scan, and the display shows devices attached to each port.

HELP! and thanks much

If you unplug all USB devices then plug in a single flash drive to each of the USB ports do 2 of the ports still not work?
Does the laptop manual state that each USB port will deliver the full 500mA. If not then you may need a powered external hub. I find the Logitech a good one.
You should also note that external USB powered HDD will probably require the full port power. I find no problems plugging them into a powered hub but I would plug your logitech unifier directly into a laptop port.