External drive gives "Access denied" on reboot.

I have an external drive (2Tb, Toshiba, USB3) which I wiped (formatted and created new volume on). I run Win7Pro64. The drive seemed to be working fine, until I rebooted, Then I got "Access denied" when I wanted to explore its contents. When I then tried to give the drive another label (in this case from M:\ to N:\) it again worked. Also when switching back to M:\ worked. However, when I reboot, I again get "Access denied".

In safe mode, the drive seems to work fine.

Any clue as to why this is? Any help is greatly appreciated - this is driving me nuts.

Thanks!

Okay, so I found the solution to this myself after some struggling. My computer is an HP which comes with its own security software. It turns out the default setting is to not allow USB devices. Good to know for others who might be struggling with their HP desktops...