I am assuming what you are trying to connect to the system is a USB hdd. Sometimes the USB HDD when connected for the first time, does not appear immediately in windows explorer with a drive letter.
You may have to go to Computer - Manage - Disk Management. Check whether the new drive has appeared and then assign a free drive letter to it. Then it will appear in windows explorer and you can access it ...
System Manufacturer/Model Number Toshiba Satellite P775-S7232 OS MS Windows 7 Ultimate 64-bit SP1 CPU i5-2410M 2.3GHz (2.9GHz Turbo-Boost) Sandy Bridge 32nm Motherboard Toshiba PHRAA ver. PSBY1U-00F003 Memory 4GB+4GB Samsung DDR3 PC3-10700 (1333 MHz) Graphics Card Video Intel(R) HD Graphics Family, 1696MB available memory Sound Card Realtek High Definition Audio version=188.8.131.5223 Monitor(s) Displays 17.3 " Trubrite TFT LCD, LED Backlit Screen Resolution 1600x900 32 bit, Native support for 720P content
Keyboard Premium Raised Tile keyboard Mouse Logitech M215 wireless mouse PSU Toshiba AC/DC Adapter Case Notebook Cooling Built-in Fan Hard Drives TOSHIBA MK6476GSXN
580.614 [GB] partitioned C: 80GB and D: 500GB with hidden recovery partitons.
Spare bay for 2nd HDD but no SATA connector :-( Internet Speed Not fast enough Other Info Built-in Harman Kardon speakers with Dolby Advanced Audio, Waves MaxxAudio® 3. HDMI, 1xUSB3+3xUSB2 ports, WebCam, Battery life 4hrs 11mins, 4GB Readyboost SDHC card, WD My Book Essential Ext HDDs 2 TB, 2x1TB, My Passport SE 1TB and WDTV 1st Gen for Multimedia playing on a Sony Wega 32" LCD.
Recent addition to my toys are Asus Transformer Pad TF300T with 32GB onboard sd card + 32GB microsd card.