laptop key "B" came off

Sometimes a key will pop off if the computer has been dropped or something was blocking the key, causing it to come off. To fix this problem, look at the back of the key and make sure the hinges are in tact. If not, you need to get a replacement for the hinge. If the hinges are in good shape then try to line up the corresponding parts of the hinge to the key, press down firmly and try wobbling the key until it snaps into place. For a more detailed guide look at the troubleshooting guide for this device.