Solution 1:

Kill the ADB server (adb kill-server) and Delete the folder: %USERPROFILE%/.android (ex: C:UsersAdministrator.android) , Start the ADB server (adb start-server)

Solution 2:

On your phone, Change the USB mode from MTP to Camera and back to MTP

Solution 3:

1 - Go to system properties
2 - look at hardware devices
3 - Right click on the yellow (has to be yellow if it's driver problem) icon representing your mobile device
4 - select property
5 - Then go on the driver tab
6 - select update driver
7 - choose the bottom selection find on local computer
8 - then choose manually
9 - From the windows opened look for driver disk the bottom right button
10 - Choose the driver from the folder <sdk>extrasgoogleusb_driveri386 (or amd64 for 64bits OS).
11 - Remember to uncheck the show only compatible hardware.
12 - Then choose the driver
13 - When windows warn your about possible incompatibility go on.

Solution 4 (For Eclipse Only, when LogCat isn't working):

1 - Open Perspective "DDMS".
2 - On the left side, click on the device.
3 - Change Perspective back to "JAVA".