Laptop will not recognise new usb device

I have a HP Pavillion dv6700 running Vista... I found that any new external harddrive or usb storage device is not recognized by my computer. I have an old western digital harddrive that works and a USB memory key that works fine.. but my new harddrive wont work or any other device new to the computer... any ideas? Iv tried downloading the drivers separately but still no luck! Even the guy in the local computer store has no idea!

Give this a try.
In device Manager, expand the USB Controller, then right click the entries and Scan for new hardware.

What "Software" was it referring to ? Digitally Signed software ensures that users can verify the origin of the software, as well as verify that no one has tampered with it. Unsigned indicates it is not original.

You may have an infection causing your problem. Run Antivirus Scan.
Also, recommend downloading Malwarebytes Antimalware Scanner, as it checks for other types of infections than the Anti Virus programs do.
And, it will not interfere with your AV application. After installation, click the update tab and get current updates, then run a quick scan.