Why does my laptop can't read the files of my nikon D3000?

Last time i have managed to upload pictures without encountering any problem. Is it because the battery is running low?

Possibly. Make sure you cameras battery is fully charged, check the connection of the usb cable, I assume you are using USB.

Check the computer listing for your camera under the heading computer (I assume you are using windows) You should see your camera on the listing as if it were an external drive (which it is).

If the camera doesn't display on your system as an external drive then you aren't completely connected.

Try rebooting the laptop with the camera powered up and connected, and see if it connects that way. Try another USB cable from another device. Try another USB device on the laptops USB port to test the port.

Battery power and USB cable are factors. But for some reason the cable is the reason. I and all the rest of the pro's would recommend a $6 accessory know as a memory card reader. I presume you have a "SD" memory card/ You just plug the USB end into an available USB outlet on your computer. (if you don't have an unused USB then get a USB "hub" (which is mutioutlet designed for USB cables). Then insert the memory card into the card reader and "presto" an icon appears on the desktop. You click the icon to get at your picture files. In one of two folders.