I have a problem while connecting my Samsung Galaxy Y Duos to my computer using a USB cable. My mobile displays "NO memory card. YOU cannot view Your photos, music etc"
I do actually have the memory card in the mobile. What can I do about this?
While the phone is connected as a USB mass storage device, it's giving the PC sole access to the SD card. The phone can't access the card at the same time because of how the USB mass storage protocol works. That's why newer Android phones use MTP instead: a different protocol that lets the phone and the PC access the SD card at the same time.
To keep the SD card available on the phone while it's connected to a PC, change the USB connection settings so that the phone is not acting as a USB mass storage device. I don't know exactly how the settings work on that phone, but if you click on the Connected to PC (or similar) notification it should take you to the appropriate settings page. There you can switch to MTP if your phone supports it, or to Charge only if it doesn't.