My AudioBox 44VSL crashes every time i use the USB ports in my laptop

I work on a very simple set up of a Toshiba laptop, AudioBox 44VSL and a Toshiba external hard-drive of 2 TB. It was working normally until a week ago as i was trying to record some audio and the AudioBox wouldn't show any signal. I tried to check what was the problem and came to a point where it seemed that when i use the external drive (where i have most of my virtual instruments) the AudioBox goes out of sync. As i thought to buy a new hard-drive i did a test and placed a virtual instrument in a small pen and got the same result, no midi signal and no sound. As soon as i try to access the instrument coected "via" usb the AudioBox stops working properly as she works if i just use the instruments within the laptop hard-drive. It's obviously a computer problem but i can't buy a new one now. The op. system is Windows 7 home premium the ext. hd.is Toshiba v63700-H 2TB, the daw is Cubase 5.1.1.120. Any suggestion is very appreciated. Thanks