I am using Dell Inspiron 660 instead of 620, but i encountered the same problems as you. I added a 4 port usb 3.0 pci-e card to my pc and failed so i contacted the manufacture for help. The method 4 solved my problem. Not know how about yours, i sugggest you trying them since it might be hard to wait for a Dell 620 to solve your problem. Hope these work!
Method 1:
After upgrading (or installing) Windows 8 Pro or Enterprise, if you find your USB 2.0 ports work but your 3.0 don't, you need to:
1. Uninstall: Step 1 is to uninstall and remove ALL third party USB 3.0 drivers;
2. Reboot: After uninstalling and removing all 3rd party USB 3.0 drivers, reboot your computer;
3. WAIT: Now, you simply wait 3 to 5 minutes for Windows 8 to detect and build drivers for your USB 3.0 devices/ports.
Method 2:
Run the Hardware and devices troubleshooter to diagnose the exact issue.
Refer the link “Open the Hardware and Devices troubleshooter” to run the troubleshooter.
Method 3:
I would suggest you to check in the Device Manager for the Device entry with SBRE. Once you find the device, uninstall the device by following this step:
a. Click on “start” button.
b. Type “Device Manager” in the search box and hit enter.
c. If you're prompted for an administrator password or confirmation, type the password or provide confirmation.
d. Click on “View” tab and select “Show Hidden devices”.
e. Check if you find any device with exclamation mark on it.
f. If so, right click on it and select “Uninstall”.
Once you uninstall the device, restart the computer for changes to take effect.
Method 4:
Once you restart the computer, download the drivers for the hardware from the Manufacturer’s website, then install it and then check if this fixes the issue.
Step 1: Some Windows 7/8 does not have native USB 3.0 drivers so to use any USB 3.0 port you must check your motherboard manufacture website for the latest USB 3.0 driver:
If your motherboard is REV 3.0, then you need to download NEC USB 3.0 controllers driver, on the other hand if it is REV 3.1, then you need the ASMedia USB 3.0 controllers driver.
a. (Intel) NEC USB 3.0 controllers driver
http://downloadcenter.intel.com/Detail_Desc.aspx?DwnldID=19880
b. (ASUS) ASMedia USB 3.0 controllers driver
http://support.asus.com/Download.aspx?SLanguage=en&m=USB3.0&p=3&os=30
Step 2: You also need to check the part number of your pci-e card chipset to download the latest usb 3.0 driver
And i really appreciat this manufacture's customer support so i am willing to help them spread their words!
http://www.newegg.com/Product/Product.aspx?Item=9SIA1HD0K30935