My cable doesn't read my USB Storage?

I have a Lenovo tablet
i connected it to my computer with my cable and it read the USB storage and SD card
while it was connected to PC i connected me external hard in another plug at the same time
now the cable doesn't read my USB storage
it reads only the SD card

What do i do now?

Added (1). i forgot to say that i found that some of the application when i touch to open it the tablet say " app isn't installed "!

Tablets generally do not handle directly connected storage devices over USB.

On the tablet, to access (or at least read) external storage attached to USB, you probably need

1. An OTG cable
I believe I got this inexpensive one
http://www.amazon.com/...0091QLXW8/

2. And this app
ES File Explorer
(Nexus tablets instead use Nexus Media Importer)

You may only be able to connect the tablet to one external storage device OR a PC at one time.

About a Lenovo Ideatab
"We connected a USB drive through a USB On-The-Go cable to check for native support. The tablet was able to instantly recognize the drive and we were able browse, save and transfer files with the ES File Explorer app."