A keyboard with an inoperable space bar may be dirty, damaged or not connected properly to the computer. There are simple fixes that may remedy the problem or determine if a greater problem exists.
According to Microsoft, the first thing to check on a malfunctioning keyboard is the keyboard's USB connection to the computer. Users should make sure it is properly seated, and if a wireless keyboard is being used, batteries in the keyboard should be checked to make sure they have a sufficient charge.
If the connection is fine, there may be a problem with dirt or grime interfering with the contact point between the keyboard key and its internal mechanism. Inverting the keyboard and tapping it on the sides and the back should dislodge any debris that exists. Using compressed air to blow out any debris may also help, but this should not be done if liquid has just been spilled onto the keyboard. Using compressed air on a wet keyboard can drive the liquid deeper into the electronics and cause more damage.
Sometimes the problem can be with a stuck key. Tapping the keyboard gently against a tabletop can often dislodge stuck keys.
If none of these tips helps, the keyboard may be damaged and in need of repair.